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THE    CHEMICAL   EFFECTS 

OF  ALPHA  PARTICLES 

AND  ELECTRONS 


BY 
SAMUEL  C.   LIND,   Ph.D. 

PHYSICAL    CHEMIST,    U.   S.    BUREAU   OF  MINES 


American  Chemical  Society 
Monograph  Series 


BOOK  DEPARTMENT 
The  CHEMICAL  CATALOG  COMPANY,  Inc. 

ONE  MADISON  AVENUE,  NEW  YORK,  U.  S.  A. 
1921 


LIBRARY 
iUOVEKSITY  OF  CALIFORNIA 


Copyright,  1921,  By 

The  CHEMICAL  CATALOG  COMPANY,  Inc. 

All  Rights  Reserved 


Press  of 

J.  J,  Little  &  Ives  Company 

New  York,  U.  S.  A. 


GENERAL  INTRODUCTION 

American   Chemical  Society  Series  of 
Scientific  and  Technologic  Monographs 

By  arrangement  with  the  Interallied  Conference  of  Pure  and 
Applied  Chemistry,  which  met  in  London  and  Brussels  in  July, 
1919,  the  American  Chemical  Society  was  to  undertake  the  pro- 
duction and  publication  of  Scientific  and  Technologic  Mono- 
graphs on  chemical  subjects.  At  the  same  time  it  was  agreed 
that  the  National  Research  Council,  in  cooperation  with  the 
American  Chemical  Society  and  the  American  Physical  Society, 
should  undertake  the  production  and  publication  of  Critical 
Tables  of  Chemical  and  Physical  Constants.  The  American 
Chemical  Society  and  the  National  Research  Council  mutually 
agreed  to  care  for  these  two  fields  of  chemical  development.  The 
American  Chemical  Society  named  as  Trustees,  to  make  the  nec- 
essary arrangements  for  the  publication  of  the  monographs, 
Charles  L.  Parsons,  Secretary  of  the  American  Chemical  Society, 
Washington,  D.  C;  John  E.  Teeple,  Treasurer  of  the  American 
Chemical  Society,  New  York  City;  and  Professor  Gellert  Alle- 
man  of  Swarthmore  College.  The  Trustees  have  arranged  for 
the  publication  of  the  American  Chemical  Society  series  of  (a) 
Scientific  and  (b)  Technologic  Monographs  by  the  Chemical 
Catalog  Company  of  New  York  City. 

The  Council,  acting  through  the  Committee  on  National  Pol- 
icy of  the  American  Chemical  Society,  appointed  the  editors, 
named  at  the  close  of  this  introduction,  to  have  charge  of  secur- 
ing authors,  and  of  considering  critically  the  manuscripts  pre- 
pared. The  editors  of  each  series  will  endeavor  to  select  topics 
which  are  of  current  interest  and  authors  who  are  recognized  as 
authorities  in  their  respective  fields.  The  list  of  monographs  thus 
far  secured  appears  in  the  publisher's  own  announcement  else- 
where in  this  volume. 

The  development  of  knowledge  in  all  branches  of  science,  and 


\^^\ 


4  GENERAL  INTRODUCTION 

especially  in  chemistry,  has  been  so  rapid  during  the  last  fifty 
years  and  the  fields  covered  by  this  development  have  been  so 
varied  that  it  is  difficult  for  any  individual  to  keep  in  touch  with 
the  progress  in  branches  of  science  outside  his  own  specialty. 
In  spite  of  the  facilities  for  the  examination  of  the  literature 
given  by  Chemical  Abstracts  and  such  compendia  as  Beilstein's 
Handbuch  der  Organischen  Chemie,  Richter's  Lexikon,  Ostwald's 
Lehrbuch  der  Allgemeinen  Chemie,  Abegg's  and  Gmelin-Kraut's 
Handbuch  der  Anorganischen  Chemie  and  the  English  and 
French  Dictionaries  of  Chemistry,  it  often  takes  a  great  deal  of 
time  to  coordinate  the  knowledge  available  upon  a  single  topic. 
Consequently  when  men  who  have  spent  years  in  the  study  of 
important  subjects  are  willing  to  coordinate  their  knowledge 
and  present  it  in  concise,  readable  form,  they  perform  a  service 
of  the  highest  value  to  their  fellow  chemists. 

It  was  with  a  clear  recognition  of  the  usefulness  of  reviews 
of  this  character  that  a  Committee  of  the  American  Chemical 
Society  recommended  the  publication  of  the  two  series  of  mono- 
graphs under  the  auspices  of  the  Society. 

Two  rather  distinct  purposes  are  to  be  served  by  these  mono- 
graphs. The  first  purpose,  whose  fulfilment  will  probably  render 
to  chemists  in  general  the  most  important  service,  is  to  present 
the  knowledge  available  upon  the  chosen  topic  in  a  readable 
form,  intelligible  to  those  whose  activities  may  be  along  a  wholly 
different  line.  Many  chemists  fail  to  realize  how  closely  their 
investigations  may  be  connected  with  other  work  which  on  the 
surface  appears  far  afield  from  their  own.  These  monographs 
will  enable  such  men  to  form  closer  contact  with  the  work  of 
chemists  in  other  lines  of  research.  The  second  purpose  is  to 
promote  research  in  the  branch  of  science  covered  by  the  mono- 
graph, by  furnishing  a  well  digested  survey  of  the  progress  al- 
ready made  in  that  field  and  by  pointing  out  directions  in  which 
investigation  needs  to  be  extended.  To  facilitate  the  attain- 
ment of  this  purpose,  it  is  intended  to  include  extended  references 
to  the  literature,  which  will  enable  anyone  interested  to  follow 
up  the  subject  in  more  detail.  If  the  literature  is  so  voluminous 
that  a  complete  bibliography  is  impracticable,  a  critical  selec- 
tion will  be  made  of  those  papers  which  are  most  important. 

The  publication  of  these  books  marks  a  distinct  departure  in 
the  policy  of  the  American  Chemical  Society  inasmuch  as  it  is  a 


GENERAL  INTRODUCTION  5 

serious  attempt  to  found  an  American  chemical  literature  with- 
out primary  regard  to  commercial  considerations.  The  success 
of  the  venture  will  depend  in  large  part  upon  the  measure  of  co- 
operation which  can  be  secured  in  the  preparation  of  books  deal- 
ing adequately  with  topics  of  general  interest;  it  is  earnestly 
hoped  therefore  that  every  member  of  the  various  organizations 
in  the  chemical  and  allied  industries  will  recognize  the  impor- 
tance of  the  enterprise  and  take  sufficient  interest  to  justify  it. 


AMERICAN   CHEMICAL   SOCIETY 

BOAED  OF  EDITOES 

Scientific  Series: —  Technologic  Series: — 

William  A.  No  yes,  Editor,  John  Johnston,  Editor, 

Gilbert  N.  Lewis,  C.  G.  Derick, 

Lafayette  B.  Mendel,  William  Hoskins, 

Arthur  A.  Noyes,  F.  A.  Lidbury, 

Julius  Stieglitz.  Arthur  D.  Little, 

C.  L.  Reese, 

C.   P.   TOWNSEND. 


American  Chemical  Society 

MONOGRAPH    SERIES 

Other  monographs  in  the  series  of  which  this  book  is  a  part 
are  in  process  of  being  printed  or  written.  They  will  be  uni- 
form in  size  and  style  of  binding.  The  list  up  to  December 
First,  1920,  includes: 

The  Animal  as  a  Converter. 

By  Henry  Prentiss  Armsby.  About  250  to  300  pages, 
illustrated. 

The  Chemistry  of  Enzyme  Actions. 

By  K.  George  Falk.    136  pages.    Notv  ready. 

The  Properties  of  Electrically  Conducting  Systems. 
By  Charles  A.  Kraus.    About  400  pages,  illustrated. 

Carotinoids  and  Related  Pigments:  The  Chromolipins. 

By  Leroy  S.  Palmer.    About  200  pages,  illustrated. 

Thyroxin. 

By  E.  C.  Kendall. 

The  Properties  of  Silica  and  the  Silicates. 

By  Robert  B.  Sosman.    About  500  pages,  illustrated. 

Organic  Mercury  Compounds. 

By  Frank  C.  Whitmore.     About  300  pages. 

Coal  Carbonization. 

By  Horace  C.  Porter.    About  475  pages,  illustrated. 

The  Corrosion  of  Alloys. 
By  C.  G.  Fink. 

Industrial  Hydrogen. 

By  Hugh  S.  Taylor.     About  200  pages,  illustrated. 

The  Vitamines. 

By  H.  C.  Sherman.     About  200  pages,  illustrated. 

For  additional  information  regarding  this  series  of  mono- 
graphs, see  General  Introduction,  page  3.  As  the  number  of 
copies  of  any  one  monograph  will  be  hmited,  advance  orders 
are  solicited. 

The  CHEMICAL  CATALOG  COMPANY,  Inc. 

OiNE  MADISON  AVENUE,  NEW  YORK,  U.  S.  A. 


AUTHOR'S  PREFACE 

In  the  decade  preceding  the  recent  European  war,  the  sub- 
ject of  photochemistry  first  began  to  receive  attention  commen- 
surate with  its  great  importance.  The  experimental  and  theo- 
retical aspects  of  the  subject  were  presented  in  the  well-known 
works  of  Plotnikow,  Weigert,  Sheppard,  Benrath,  and  others. 

The  chemical  effects  produced  by  some  of  the  other  forms  of 
radiant  energy  or  matter  have  also  been  investigated,  more  or 
less  fully,  but  the  experimental  results  in  this  field  have  not 
hitherto  been  brought  together  in  monographic  form.  The  chemi- 
cal effects  of  the  various  kinds  of  corpuscular  radiation  may  be 
regarded  as  constituting  one  division  of  the  general  subject  of 
radio  chemistry  (as  defined  in  this  monograph),  of  which  photo- 
chemistry proper  forms  another  division.  The  various  effects, 
such  as  those  of  a  and  p  particles,  high  velocity  electrons,  posi- 
tive rays,  recoil  atoms,  etc.,  have  been  regarded  as  being  so  in- 
directly related  either  to  photochemistry  or  to  radioactivity,  that 
they  have  received  rather  scant  treatment  in  the  standard 
treatises  on  those  two  subjects. 

It  is  the  object  of  this  monograph  to  collect  the  experimental 
material  and,  as  far  as  possible,  to  present  it  in  such  a  way  as 
to  emphasize  the  relations  between  the  chemical  effects  of  the 
material  and  of  the  photochemical  radiations.  The  theoretical 
development  has  also  been  carried  as  far  as  the  available  data 
permit  at  the  present  time.  In  the  main,  however,  the  subject 
is  still  in  the  empirical  stage  and  must  await  further  evidence 
as  to  the  behavior  of  individual  atoms  and  gaseous  ions  before 
final  conclusions  can  be  drawn  regarding  the  exact  mechanisms 
of  the  radiochemical  reactions. 

The  field  of  photochemistry  has  been  touched  upon,  in  the 
present  work,  only  in  comparing  the  nature  of  the  various  radio- 
chemical effects,  and  also  in  connection  with  the  Einstein  photo- 
chemical equivalence  law,  which  shows  a  close  analogy  with  the 
ionic-chemical   equivalence   of  the   corpuscular  radiant  effects. 

7 


8  AUTHOR'S  PREFACE 

A  fairly  full  consideration  of  the  experimental  tests  of  the  photo- 
chemical equivalence  law  appeared  to  have  additional  justifica- 
tion, from  the  fact  that  the  recent  evidence  has  not  yet  been 
treated  in  the  standard  texts  of  photochemistry. 

The  subject  of  radioactivity  has  been  introduced  only  in  so 
far  as  was  necessary  to  afford  an  insight  into  the  principles  artd 
technique  involved  in  the  utilization  of  radioactive  substances 
as  sources  of  radiation  in  the  production  of  the  chemical  ef- 
fects under  consideration.  For  the  radioactive  data  included  in 
this  monograph,  the  writer  is  indebted  to  the  following  texts: 
Rutherford's  "Radioactive  Substances  and  Their  Radiations" 
(1913),  Mme.  Curie's  "Traite  de  Radioactivite"  (1910),  Meyer 
and  V.  Schweidler's  "Radioaktivitat"  (1916),  Bragg's  "Studies  in 
Radioactivity"  (1912),  and  to  J.  J.  Thomson's  "Rays  of  Posi- 
tive Electricity"  (1913). 

The  writer  is  also  greatly  indebted  to  the  cooperation  of  the 
Editors  of  the  Scientific  Monographs  of  the  American  Chemical 
Society,  who  have  supervised  the  publication  of  the  present  mono- 
graph, to  Dr.  G.  L.  Wendt  of  the  University  of  Chicago  for 
his  very  helpful  suggestions  and  criticisms,  and  to  the  Chemical 
Catalog  Company,  Inc.,  which  has  efficiently  carried  out  the 
plans  of  the  Editors. 


CONTENTS 

PAGE 

Chapter  1.     Radiochemistry 17 

1.  Definition  of  Radiochemistry. — 2.  Radiant  Energy 
and  Matter. — 3.  Photo-  and  Radio-Chemistry. 

Chapter  2.    Brief  Outline  of  Radioactivity  and  Some 

Properties  of  the  Radiations 20 

4.  Nature  of  Radioactivity — Rutherford-Soddy  Hy- 
pothesis.— 5.  Radioactive  Phenomena. — 6.  Kinds  of 
Radiation. — 7.  Radioactive  Families  and  their  Trans- 
formation Products. — 8.  Radioactive  Equilibrium. — 
9.  Kinetic  Energy  of  a  Particles. — 10.  Range  of  a 
Particles. — 11.  Ionizing  Power  of  a  Particles. — 12. 
Enumeration  of  a  Particles. — 13.  Some  Additional 
Properties  of  a  Particles. — 14.  Characteristics  of 
Members  of  the  Radium  Family  as  Sources  of  Radia- 
tion. 

Chapter  3.     Electrical  Effects — Ionization         .        .      37 

15.  Saturation  Current  as  a  Measure  of  Ionization. — 

16.  Ionization  by  Electronic  Shock. — 17.  Some  Prop- 
erties of  p  Particles  and  Electrons. — 18.  y  Rays  and 
X  Rays. 

Chapter  4.  Qualitative  Radiochemical  Effects  .  .  46 
19.  General  Classification. — 20.  Qualitative  Observa- 
tions.— 21.  Coloration  and  Decomposition  of  Radium 
Salts. — 22.  Coloration  of  Glass  and  Minerals. — 23. 
Thermo-luminescence  produced  by  Radiation. — 24. 
Luminescence  and  Phosphorescence  produced  by 
Radiation. — 25.  General  Character  of  the  Chemical 
Effects  of  the  Rays  of  Radium. 

Chapter  5.    Chemically  Quantitative  Investigations  in 

Liquid  Systems 59 

26.  Decomposition  of  Water  by  Radium  Salts  in 
Solution. — 27.  Formation  of  Hydrogen  Peroxide  in 
Water. — 28.  Reactions  produced  by  Penetrating  Rays. 

.9 


10  CONTENTS 


PAGE 


Chapter  6.    Reactions  Produced  by  Radium  Emana- 
tion.    (First  Experiments) 65 

29.  Radium  Emanation  as  a  Source  of  Radiation. — 30. 
Experiments  of  Cameron  and  Ramsay. — 31.  Experi- 
ments of  Usher  on  the  Ammonia  Equilibrium. 

Chapter  7.    Relation  between  Gaseous  Ionization  and 

Radiochemical  Effects 74 

32.  Historical  Development  of  the  Ionization  Theory 
of  the  Chemical  Effects  of  Corpuscular  Radiation. — 

33.  Production  of  Ozone  by  a  Particles. — 34.  Other 
Gas  Reactions. — 35.  Calculation  of  the  Average  Path 
of  a  Particles. — 36  Results  of  Various  Investigations. 
37.  Reactions  in  Liquid  Systems — Results  of  Duane 

•  and  Scheuer  on  the  Decomposition  of  Water,  Ice  and 
Water  Vapor. — 38.  Experiments  of  Scheuer  on  the 
Formation  of  Water  by  a  Radiation. — 39.  Experi- 
ments of  Wourtzel  on  the  Decomposition  of  Gases. 

Chapter  8.    Kinetics  of  the  Chemical  Reactions  Pro- 
duced BY  Radium  Emanation 94 

40.  Classification  of  the  Reactions. — 41.  Development 
of  General  Kinetic  Equation  for  the  Action  of  Emana- 
tion when  Mixed  with  Gases  in  Small  Volumes. — 42. 
Application  of  Kinetic  Equation  to  Experimental  Re- 
sults.— 43.  Influence  of  the  Size  of  the  Reaction  Vessel, 
Law  of  the  Inverse  Square  of  the  Diameter  of  the 
Sphere. — 44.  Use  of  Kinetic  Results  to  Evaluate  M/N. 

Chapter  9.     Additional  Relationships  of  the  Radio- 
chemical Effects 107 

45.  Influence  of  Varying  the  Proportions  of  Hydrogen 
and  Oxygen. — 46.  Action  of  a  Rays  on  Pure  Oxygen 
or  Pure  Hydrogen. — 47.  Comparison  of  the  Chemical 
Effects  of  a  and  of  Penetrating  Rays. — 48.  General 
Discussion  of  Ionic-Chemical  Equivalence. — 49.  Ex- 
ceptions to  Ionic-Chemical  Equivalence,  Reactions  in 
which  M  exceeds  N. — 50.  Reactions  in  which  N  ex- 
ceeds M. — 51.  Energy  Utilization  of  a  Rays  in 
Chemical  Reactions. — 52.  Chemical  Reaction  Pro- 
duced by  Electrical  Discharge  in  Gases. — 53.  Produc- 
tion of  Free  Electrical  Charges  by  Chemical  Action. 

Chapter  10.    Photochemical  Equivalence  Law      .        .     132 
54.  Einstein's  Application  of  the  Quantum  Theory  to 
Photochemical  Action. — 55.  Experimental  Tests  of  the 


CONTENTS  11 

PAGE 

Law  of  Photochemical  Equivalence. — 56.  Comparison 
of  Photochemical  Equivalence  Law  and  Ionic-Chemical 
Equivalence. — 57.  Mechanism  Proposed  by  Nernst  for 
the  Hydrogen-Chlorine  Photo-Reaction. — 58.  General 
Radiation  Theory  of  Chemical  Action. 

Chapter  11.  Positive  Rays  and  Recoil  Atoms  .  .  148 
59.  General  Nature  of  Positive  Rays. — 60.  Thomson's 
Method  of  Positive  Ray  Analysis. — 61.  Isotopes  of 
Neon. — 62.  Discovery  of  Other  New  Isotopes  by  Aston. 
— 63.  General  Properties  of  Recoil  Atoms. — 64. 
Chemical  Reaction  produced  by  Recoil  Atoms. 

Chapter  12.    Atomic  Disintegration  by  a  Particles      .     162 
65.  Scattering  and  Impacts  of  a  Particles. — 66.  Swift 
Hydrogen  Atoms. — 67.  Decomposition  of  Nitrogen  and 
Oxygen. — 68.  Experiments  of  Rutherford  with  Other 
Light  Atoms. — 69.  Artificial  Radioactivity. 

Index  of  Subjects 173 

Index  of  Authors 178 


TABLES 

Subject 

NUMBER  PAGB 

I.    Uranium-Radium   Series 28 

II.    Stopping  Power  and  Ionization  of  a  Particle        .      33 

III.  Decomposition  of  Water  by  Emanation    (Cam- 

eron and  Ramsay) 69 

IV.  Formation    of    Water     (Moist)     by    Emanation 

(Cameron  and  Ramsay) 71 

V.    Formation  of  Water  (Dry)  by  Emanation  (Cam- 
eron and  Ramsay) 72 

VI.    Radiometric  Method  to  Determine  Range  of  a 

Particles 78 

VII.    Chemical-Ionic  Equivalence   (M/N)     .        .         85,86 

VIII.    Decomposition  of  Water,  Ice,  and  Water  Vapor 

(Duane  and  Scheuer) 89 

IX.    Decomposition  of  Gases  by  Emanation  (Wourtzel)       93 

X.    Application  of  Kinetic   Equation   to   Results  of 

Cameron  and  Ramsay       .        .        .        .         97,98 

XI.    Application  of  Kinetic  Equation  to  Results  of 

Lind   . 99 

XII.    Effect  on  the  Velocity  Constant  of  Varying  the 

Diameter 101 

XIII.    Effect   on   the  Velocity   Constant   of   Excess   of 

Hydrogen 109 

XIV.    Effect  on  the  Velocity   Constant  of  Excess   of 

Oxygen 110 

XV.    Primary  Light  Reactions    (Bodenstein)        .        .     134 

XVI.    Secondary  Light  Reactions  (Bodenstein)       .      137, 138 

13 


14  TABLES 

NUMBER  CAQB 

XVII.    Test    of    Einstein's    Photochemical    Equivalence 

Law   (Frl.  Pusch) 139 

XVIII.    List  of  New  Isotopes  by  Positive  Ray  Method 

(Aston) 153 

XIX.     Chemical  Effect  of  Recoil  Atoms — Data  and  Cal- 
culations   (Lind) 157 

XX.    Analysis  of  Recoil  Atom  Effect   (Lind)      .        .     160 

Appendix 

A.  Rate    of    Decay    of    Radium    Emanation,    e"^' 

(Kolowrat) 170-171 

B.  Radioactive  Isotopes   (Fajans)      ....    172 


ILLUSTRATIONS 

NUMBER  Subject 

OF  FIG.  PAGE 

1.  Ionization  Curve  of  an  a  Particle     ....      30 

2.  Curve  of  Saturation  Current  and  of  Ionization  by- 

Electronic  Shock 38 

3.  Apparatus  of  Cameron  and  Ramsay  for  Gas  Re- 

actions  (Emanation) 67 

3a.  Apparatus  of  Cameron  and  Ramsay  for  the  Decom- 
position of  Water 67 

4.  Apparatus  of  Camerpn  and  Ramsay  for  Various  Re- 

actions      68 

5.  Diagram  for  the  Calculation  of  the  Average  Path 

of  a  Particles  in  a  Sphere  of  Diameter  less  than 

the  Range  (Lind) 82 

6.  Apparatus  for  the  Combination  of  Hydrogen   and 

Oxygen   (Emanation) 100 

7.  Curves    showing    the    Chemical    Effect    of    Recoil 

Atoms    (Lind) 158 


THE  CHEMICAL  EFFECTS  OF 
ALPHA  PARTICLES  AND  ELECTRONS 


Chapter  1. 
Eadiochemistry. 

1.    Definition  of  Radiochemistry. 

The  relationships  existing  between  the  various  forms  of 
energy  and  the  transformations  of  the  different  kinds  into  one 
another  are  of  fundamental  importance  in  the  physical  sciences. 
The  chemist  is  primarily  concerned  with  those  transformations 
in  which  chemical  energy  is  one  of  the  forms  involved.  Thermo- 
and  electro-chemistry  represent  two  of  the  most  highly  devel- 
oped branches  of  physical  chemistry  and  deal  with  the  relations 
between  chemical  energy  on  the  one  hand  and  thermal  and  elec- 
trical energies,  respectively,  on  the  other.  Of  no  less  importance 
are  the  relations  between  chemical  and  radiant  energies,  which 
constitute  a  subject  that  should,  according  to  the  same  system 
of  terminology,  be  designated  as  radiochemistry. 

The  term  radiochemistry  has  already  been  used  otherwise  by 
some  authors  to  designate  the  chemistry  of  the  radioactive  ele- 
ments and  of  their  transformations  by  atomic  disintegration. 
Since  this  more  special  usage  is  relatively  new  and  not  thoroughly 
intrenched,  and  since  the  term  radiochemistry  is  the  only  logical 
one  to  conform  with  such  terms  as  electro-,  thermo-,  photo- 
chemistry and  radiotherapy,  it  appears  desirable  to  adopt  the 
use  of  the  term  radiochemistry  in  the  broader  sense,  exactly 
analogous  to  and  including  that  of  photochemistry,  in  the  sense 
that  all  relations  between  chemical  energy  and  any  form  of 
radiant  energy  or  matter  should  be  comprehended  by  the  term 
radiochemistry. 

17 


18  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

2.  Radiant  Energy  and  Matter. 

In  the  strictest  sense,  perhaps,  radiochemistry  should  deal 
only  with  truly  radiated  energy  to  the  exclusion  of  the  kinetic 
energy  of  projected  particles  of  matter  such  as  a  particles  or  of 
electrons  and  [3  particles.  This  would  practically  narrow  the 
subject  to  that  of  photochemistry  itself.  It  is  not  only  a  matter 
of  convenience  to  include  also  the  relations  involving  material 
particles,  but  the  relationships  and  reactions  are  in  many  ways 
so  similar,  and  the  analogies  of  such  far-reaching  importance, 
that  it  forms  one  of  the  chief  objects  of  the  present  work  to 
treat  both  from  the  same  standpoint,  without  any  particular 
distinction  as  to  the  vehicle  of  the  radiated  energy. 

The  forms  of  radiant  energy  or  matter  to  which  attention  will 
be  given  are:  a  and  p  particles,  y  rays,  recoil  atoms,  positive 
rays,  electrons  including  the  various  forms  of  electrical  discharge 
such  as  corona,  silent  and  spark  discharges,  and,  to  a  certain  ex- 
tent, visible  and  ultraviolet  light  and  X  rays.  The  differentia- 
tion in  terms  involved  in  the  usage  a  or  |3  particle  and  y  ray 
will  not  be  adhered  to  strictly.  For  the  sake  of  brevity,  free 
use  will  be  made  of  the  older  terms  a  and  p  rays. 

3.  Photo-  and  Radio-Chemistry. 

A  full  appreciation  of  the  vastly  important  function  of  light 
in  our  terrestrial  economy,  both  past  and  present,  in  transform- 
ing and  storing  chemical  energy  will  serve  to  emphasize  the  im- 
portance of  photochemistry.  While  it  can  not  be  claimed  that 
either  the  recognition  of  the  relative  position  of  photochemistry 
or  the  actual  beginning  of  the  science  is  new,  it  is  only  within 
the  decade  preceding  the  recent  European  war  that  its  develop- 
ment may  be  regarded  as  commensurate  with  its  preeminent  im- 
portance. Compared  with  the  state  of  development  in  thermo- 
or  electro-chemistry,  photochemistry  must  be  conceded  to  be  in 
its  beginning  and  not  yet  past  the  first  stages  of  empiricism. 

It  appears  unnecessary  to  seek  far  afield,  as  some  authors 
have  done,  for  the  causes  of  the  slow  development  of  photo- 
chemistry. The  earlier  development  of  one  of  its  technical 
branches,  photography,  doubtless  contributed  to  the  neglect  of  the 
mother  science,  as  has  been  suggested  by  Luther,^  but  other  con- 

» B.  Luther,  Bunsengcsellsch.  1908 ;  Zoit.  f.  Elcktrochcm.,  U,  445-53. 


RADIOCHEMISTRY  19 

tributing  factors  demand  consideration,  such  as  the  difficulties 
presented  by  the  intricate  technique  of  photochemical  experimen- 
tation, the  necessity  of  awaiting  progress  in  the  sciences  of  radi- 
ology and  of  atomic  structure,  and  also  the  early  unfortunate 
overemphasis  of  the  catalytic  nature  of  photochemical  phe- 
nomena. 

As  has  been  stated  in  the  preface  several  treatises  have  ap- 
peared which  deal  very  adequately  with  the  subject  of  photo- 
chemistry. It  is  not  the  purpose  of  the  present  monograph  to 
duplicate  this  field,  but  rather  to  attempt  to  extend  it  by  pre- 
senting the  experimental  results  of  the  investigation  of  chemical 
reactions  brought  about  by  some  other  forms  of  radiant  energy, 
such  as  electrical  and  radioactive  discharges,  with  the  object  of 
pointing  out  those  analogies  an"d  differences  which  appear  to 
exist. 

The  general  subject  of  radiochemistry  is,  like  photochemistry, 
still  in  the  experimental  stage  and  must  be  approached  from  the 
empirical  side  without  any  expectation  of  arriving  at  once  at 
final  principles.  It  is  therefore  the  object  of  this  work  to  present 
the  experimental  results  for  the  chemical  effects  of  some  of  the 
other  forms  of  radiant  energy  than  light  in  the  hope  that  their 
examination  and  comparison  with  the  results  of  photochemical 
investigations  may  contribute  to  a  somewhat  more  comprehen- 
sive view  of  the  field  of  radiochemistry  as  a  whole.  Although 
the  branch  of  radiochemistry  to  be  treated  is  of  recent  develop- 
ment and  has  been  open,  on  account  of  the  scarcity  of  some  of 
the  necessary  radioactive  material,  only  to  a  limited  number  of 
investigators,  nevertheless,  very  definite  results  have  been  ob- 
tained for  a  few  reactions  and  some  principles  have  been  estab- 
lished that  appear  to  have  fairly  general  applicability. 


Chapter  2. 

Brief  Outline  of  Eadioaetivity  and  Some  Properties 
of  the  Radiations. 

4.    Nature  of  Radioactivity — Rutherford-Soddy  Hypothesis. 

While  it  lies  outside  the  province  of  radiochemistry  to  con- 
sider the  subject  of  radioactivity  in  its  entirety,  it  is  impos- 
sible to  treat  the  chemical  effects  of  the  radiations  accompany- 
ing and  produced  by  radioactive  changes  without  giving  some  at- 
tention to  the  various  radioactive  elements  and  their  radiations. 

Historically  it  is  interesting  to  recall  that  the  discoveries 
both  of  X  rays  by  Roentgen  and  of  radioactive  radiations  by 
Becquerel  were  made  through  the  means  of  their  radiochemical 
actions  on  the  photographic  plate.  Although  other  more  con- 
venient methods  of  investigation  were  soon  developed,  the  photo- 
graphic method  has  continued  to  play  a  role  of  some  impor- 
tance. 

The  continuous  emission  of  heat  and  of  radiations  was  one 
of  the  first  properties  of  radioactive  substances  to  be  observed, 
and  also  proved  to  be  one  of  the  most  puzzling  since  it  appeared 
to  contravert  the  law  of  the  conservation  of  energy.  In  looking 
for  a  general  theory  of  radioactivity  it  appeared  to  Pierre  Curie 
and  A.  Laborde  ^  not  impossible  that  radioactive  matter  might 
be  merely  the  receptor  of  a  form  of  radiant  energy  coming  from 
extraterrestrial  sources  and  capable  of  affecting  only  the  ele- 
ments of  heaviest  atomic  weight.  To  ascertain  if  the  sun  might 
be  the  source  of  the  supposed  radiant  energy,  comparison  was 
made  of  the  activity  of  a  radioactive  substance  measured  at  noon 
and  again  at  midnight  to  find  if  the  interposition  of  the  earth's 
thickness  would  diminish  the  activity.  A  negative  result  was 
obtained. 

Although  it  was  early  suggested  that  radioactivity  is  purely 
an  atomic  phenomenon,  it  was  not  until  1903  that  Rutherford 

»P.  Curie  and  A.  Laborde,  Comp.  rend.,  13G,  G73   (1903). 

20 


SklEP  OtJTLINE  OF  RADtOActlVlTY  ^1 

and  Soddy  ^  proposed  and  elaborated  a  concrete  theory  of  suc- 
cessive atomic  disintegration  which  explained  all  the  phenomena 
exhibited  by  radioactive  substances,  and  left  no  doubt  that  the 
source  of  radioactive  energy  and  radiation  is  from  within  the 
radioactive  atom  itself.  All  subsequent  investigations  have  only 
strengthened  this  hypothesis,  until  now  it  is  supported  by  a  chain 
of  evidence,  both  experimental  and "  theoretical,  which  is  unique 
in  its  completeness  and  perhaps  without  parallel  in  the  physical 
sciences. 

5.  Radioactive  Phenomena. 

Radioactive  substances  exhibit  the  following  striking  prop- 
erties : 

(1)  The  continuous  emission  of  heat. 

(2)  The  continuous  emission  of  certain  rays  and  particles. 

(3)  The  production  of  luminescent  effects  in  some  sub- 
stances. 

(4)  The  ionization  of  the  surrounding  air  (or  of  other 
gases). 

(5)  The  production  of  chemical  reaction  in  substances 
subjected  to  radiation. 

(6)  The  production  in  some  substances  of  certain  effects 
such  as  color,  thermoluminescence,  etc.,  which  may  or 
may  not  be  due  to  chemical  action. 

The  most  notable  of  these  phenomena  is  the  emission  of 
electrically  charged  particles  at  high  velocity  from  the  radio- 
active atom,  due  to  some  internal  disturbance  of  the  electrical 
equilibrium  of  the  atom,  the  cause  and  exact  nature  of  which 
are  not  yet  wholly  understood.  All  of  the  other  phenomena 
enumerated  may  be  regarded  as  secondary  effects  of  the  radia- 
tions. 

6.  Kinds  of  Radiation. 

Three  distinct  kinds  of  radiation  are  emitted  by  the  various 
radioactive  substances:  a  particles,  p  particles,  and  y  rays. 
a  Particles.    The  corpuscular  nature  of  a  particles  was  first 

'Rutherford  and  Boddy,  Phil.  Mag.  (6)  4,  370;  569  (1902),  5,  441;  576 
(1903). 


22  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

suggested  by  Mme.  Curie  ^  in  1900  to  explain  the  peculiarities 
of  their  absorption  or  loss  of  energy  in  passing  through  matter. 
Strutt*  suggested  their  being  positively  charged,  Rutherford^ 
demonstrated  their  deflection  both  by  magnetic  and  by  electrical 
fields.  Later  Rutherford  and  his  co-workers  ®  showed  that  a  par- 
ticles are  doubly  positively  charged  helium  atoms.  They  are 
emitted  from  the  radioactive  atom  at  a  very  high  initial  velocity 
(1/15  to  1/20  that  of  light),  and  since  they  possess  mass  of 
atomic  dimensions,  they  represent  an  enormous  concentration  of 
kinetic  energy.  In  fact  the  a  particle  is  the  most  powerful  agent 
yet  known  to  science  and  in  all  probability  will  remain  so,  as  it 
is  hardly  conceivable  that  any  means  will  ever  be  devised  of 
imparting  to  ponderable  matter  a  velocity  exceeding  that  at 
which  the  a  particle  is  dispelled  from  the  atomic  nucleus.  It  is 
therefore  not  surprising  that  we  find  in  the  a  particle  a  powerful 
agent  in  bringing  about  ordinary  chemical  changes  in  matter 
with  which  it  comes  into  contact,  but,  as  Rutherford^  has  re- 
cently shown,  at  least  two  kinds  of  atoms  (nitrogen  and  oxygen) 
when  squarely  struck  by  an  a  particle  are  completely  altered, 
producing  hydrogen  or  helium  atoms  (see  Chapter  XII).  Of  the 
total  energy  emitted  by  radioactive  substances,  by  far  the  larger 
proportion  is  carried  by  the  a  particles,  and  it  is  principally  the 
transformation  of  this  eniergy  that  results  in  the  production  of 
the  thermal,  electrical  and  chemical  effects  already  referred  to. 

P  Particles.  The  (3  particles  emitted  by  radioactive  matter 
have  been  proved  by  numerous  authorities  to  consist  of  elec- 
trons, singly  charged  atoms  of  negative  electricity,  ejected  from 
the  nucleus  of  the  radioactive  atom  at  varying  velocities,  in  some 
cases  approaching  closely  to  that  of  light. 

Y  Rays  for  a  long  time  presented  an  unsolved  problem  as  to 
their  exact  nature  and  origin.  They  are  emitted  only  by  sub- 
stances which  also  emit  p  particles  and  evidently  are  connected 
with  this  emission.  It  is  now  generally  conceded  that  they  con- 
sist of  ether  pulses  of  very  short  wave  length  and  therefore  have 
the  general  properties  of  light  and  may  be  most  aptly  compared 

•Mme.  Curie,  Comp.  rend.,  130,  7G  (1900). 
*R.  J.  Strutt.  Phil.  Trans.  Roy.  Soc.  A  19G,  507  (1901). 
•E.  B*  Rutherford.  PhU.  Mag.  {G)    5,  177  (1903)  ;  Phys.  Zeit.,  4,  235  (1903). 
•Rutherford   and   Geigcr,   Proc.  Roy.   Soc.  A   81,    162    (1908).   Phys.   Zeit., 
10,  42   (1909).     Rutherford  and  Royds,  Phil.  Mag.,  17,  281   (1909). 
'Rutherford,  Phil.  Mag.   (6)    37,  537-587    (1919). 


BRIEF  OUTLINE  OF  RADIOACTIVITY  23 

with  X  rays,  except  that  they  greatly  exceed  in  shortness  of 
wave  length  and  penetrating  power  any  X  rays  that  have  yet 
been  produced.  A  fuller  discussion  of  the  properties  of  these 
three  kinds  of  radiation  will  be  found  in  subsequent  paragraphs. 
Recoil  atoms  also  constitute  a  form  of  radiation  that  has  been 
shown  to  produce  chemical  effects.  A  recoil  atom  is  the  re- 
mainder of  a  radioactive  atom  just  after  the  emission  of  an  a 
(or  P)  particle  while  it  is  still  in  rapid  motion  owing  to  the  "re- 
coil" action.  Ionization  and  other  radiation  effects  are  produced. 
Further  reference  to  recoil  atoms  will  be  found  in  Chapter  XI. 

7.    Radioactive  Families  and  Their  Transformation  Products. 

Of  the  common  elements  only  two,  uranium  and  thorium, 
have  been  found  to  possess  distinct  radioactive  properties.  Each 
of  these  two  elements  is  the  parent  of  a  series  of  radioactive  ele- 
ments undergoing  atomic  decay.  There  is  also  a  third  family 
having  as  its  parent,  actinium,  an  element  of  very  rare  occur- 
rence, apparently  a  side-chain  offspring  of  the  uranium  series. 
These  three  families  comprise  about  thirty-five  members  which 
differ  from  each  other  in  chemical,  physical  and  radioactive  prop- 
erties, the  latter  being  characterized  by  the  radiations  emitted 
and  by  the  rate  of  change  of  one  element  into  the  next  lower 
member  in  the  series.  Employing  the  usual  terminology  of  chemi- 
cal kinetics,  each  simple  radioactive  change  has  proved  to  be 
mono-molecular,  and  not  only  corresponds  perfectly  to  the  re- 
quirements of  the  logarithmic  equation  of  the  so-called  first  order 
reactions,  with  respect  to  time  rate  of  change,  but  the  rate  of 
change  persists  unaltered  no  matter  to  what  physical  or  chemical 
influences  it  may  be  subjected.  A  simple  radioactive  trans- 
formation represents  par  excellence  the  first  order  reaction. 
The  rate  of  change  is  usually  formulated  as:  E=Eo.e-^*,  in  which 
Eq  is  the  initial  quantity  of  radioactive  material  undergoing 
change,  and  E  the  quantity  remaining  unchanged  after  the  lapse 
of  any  interval  of  time  t,  e  is  the  base  of  the  Naperian  logarithmic 
system,  and  X  is  the  decay  constant,  by  which  is  meant  the  frac- 
tion of  the  total  which  changes  in  unit  of  time;  l  is  the  recipro- 
cal of  6  J  the  ^'average  lije^^  of  a  radioactive  element,  which  is  not 
to  be  confused  with  the  term  "half  period"  of  the  element.  The 
half  period  is  the  time  in  which  just  one-half  of  the  initial  quan- 


24  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

tity  undergoes  change;  and,  as  is  also  the  case  for  all  first  order 
reactions,  it  makes  no  difference  what  time  or  quantity  is 
chosen  as  initial.  The  relation  between  the  two  is:  average  life 
(d)  =  half  period  x  nat,  log  2  (=  1.4428).  It  may  be  men- 
tioned that  the  usual  form  of  the  differential  equation  for  first 
order  reactions,  dx/dt  =  k(A-x)  <^)  can  be  readily  converted  into 
the  form  given  above  for  radioactive  changes.  The  average  life 
for  a  given  element  is  its  most  fundamental  physical  constant, 
and  is  found  to  vary  for  the  different  elements  from  a  very  small 
fraction  of  a  second  up  to  several  billion  years.  As  far  as  known 
the  reactions  are  irreversible. 

Uranium  and  thorium  are  the  two  elements  possessing  the 
highest  known"  atomic  weights,  and  the  property  of  radioactivity 
does  not  seem  to  be  possessed  by  elements  of  atomic  weight  less 
than  210,  excepting,  perhaps,  potassium  and  rubidium,  which 
have  been  shown  ^  to  emit  p  rays. 

According  to  the  Rutherford  and  Soddy  hypothesis  one  atom 
of  a  radioactive  substance  A  changes  to  form  one  atom  of  sub- 
stance B,  and  in  case  of  the  emission  of  a  particles,  one  atom  of 
helium  is  ejected  from  each  atom  of  A  in  changing  to  B.  It  fol- 
lows that  B  must  have  an  atomic  weight  four  units  lower  than 
that  of  A,  also  that  the  enumeration  of  the  a  particles  emitted 
serves  as  a  measure  of  the  rate  and  quantity  of  change,  and  also 
that  the  accumulation  of  helium  gas  over,  a  known  period  may 
serve  as  a  measure  of  the  same  constants;  or,  vice  versa,  if  the 
rate  of  change  be  known,  the  accumulation  of  helium  is  a  meas- 
ure of  the  period  of  time  during  which  the  accumulation  has 
taken  place.  Reference  to  the  fuller  texts  on  radioactivity  ^° 
will  show  that  all  these  factors  have  been  abundantly  verified  ex- 
perimentally and  fit  into  the  network  of  evidence  confirming 
the  Rutherford  and  Soddy  theory  of  radioactive  change. 

8.    Radioactive  Equilibrium. 

Although  the  radioactive  changes,  as  already  stated,  are  ir- 
reversible and  hence  incapable  of  attaining  a  state  of  equilibrium 

(8)  S.  L.  Bigelow,  "Thoorotical  and  Physical  Chemistry,"  p.  S.'S  (1912). 
K.  G.  Falk,  "Chemistry  of  Enzymo  Actions,"  p.  22   (1921). 

•N.  R.  Campbell  and  A.  Wood,  Proc.  Camh.  Phil  Soc,  14,  15   (1907). 

"Rutherford,  "Radioactive  Substances  and  Their  Radiations"  (1913).  Mme. 
Curie,  "Traite  de  Radioactivity"  (1910).  Meyer  and  von  Schweidler,  "Radlo- 
aktivitat"    (1916).  > 


BRIEF  OUTLINE  OF  RADIOACTIVITY  25 

in  the  ordinary  way  of  reversible  reactions,  yet  a  state  of 
dynamic  equilibrium  may  be  attained  between  a  parent  element 
and  one  or  more  of  its  decomposition  products.  This  occurs 
through  the  change  of  the  product,  not  back  into  the  original, 
but  into  new  products  at  the  same  rate  that  it  is  being  produced 
from  the  parent.  Thus  the  parent  element,  which  is  producing 
its  decay  product  at  the  same  rate  that  the  latter  is  undergoing 
further  change,  has  attained  a  state  of  dynamic  equilibrium  in 
which  a  constant  ratio  between  the  quantities  of  the  two  elements 
involved  is  maintained.  Such  radioactive  equilibrium  may  apply 
to  a  whole  family  or  to  any  part  of  a  family,  beginning  with  a 
parent  element  of  longer  life  than  its  products.  For  example, 
uranium  in  nature,  after  the  lapse  of  geological  ages,  is  found  to 
be  in  equilibrium  with  all  the  members  in  its  family.  Radium 
attains  equilibrium  with  its  next  succeeding  decay  products  in 
about  one  month,  while  radium  emanation  reaches  equilibrium 
with  its  immediate  products  in  four  hours. 

From  the  physical-chemical  standpoint  these  equilibria  rep- 
resent nothing  different  from  what  one  should  expect  from  a  se- 
ries of  successive  irreversible  mono-molecular  reactions.  By 
the  superposition  of  equations  of  the  first  order  Rutherford  ^^  has 
dealt  with  the  equilibria,  which  on  the  whole  must  be  regarded 
as  the  most  complete  series  of  successive  reactions  known  to 
physical  chemistry.  They  may  appear  intricate  on  account  of 
their  number,  but  otherwise  they  are  wonderfully  simple  and  free 
from  complications  such  as  would  arise  in  the  treatment  of  ordi- 
nary chemical  reactions. 

From  the  radioactive  standpoint  the  dynamic  equilibria  are 
of  great  importance  from  the  following  considerations:  When 
two  or  more  radioactive  elements  are  in  equilibrium,  the  number 
of  atoms  of  each  element  being  formed  and  decaying  per  unit 
of  time  is  the  same.  Throughout  a  whole  system  of  elements  in 
radioactive  equilibrium,  the  number  of  atoms  of  each  element 
changing  per  unit  time  is  identical  and  is  also  measured  by  the 
number  of  a  particles  being  emitted  per  unit  of  time  by  any 
member  of  the  system.  This  means  of  course  that  equilibrium 
quantities  of  all  elements  in  the  same  radioactive  family  emit 
the  same  number  of  a  particles  per  second.  For  example,  if  one 
gram  of  radium  emits  3.72x10^°  a  particles  per  second,  that 

"  Rutherford,  "Radioactive   Substances  and  Their  Radiations,"  Chapter  11. 


26  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

quantity  of  any  other  member  of  the  uranium  family  which 
would  be  in  equilibrium  with  one  gram  of  radium  would  also 
emit  the  same  number  of  a  particles  per  second.  This  makes  it 
evident  that  in  chosing  units  for  radioactive  elements  it  is  much 
simpler  to  deal  with  the  relative  equilibrium  quantities  rather 
than  with  absolute  masses,  particularly  since  many  of  the  radio- 
elements  can  not  be  obtained  in  ponderable  quantities  and  are 
measured  only  through  some  radiant  property.  Such  a  system 
of  units  was  devised  and  adopted  at  the  direction  of  the  Inter- 
national Congress  of  Radiology  and  Electricity,  Brussels,  1910. 
One  gram  of  elemental  radium  was  chosen  as  the  basic  unit. 
Standard  preparations  of  radium  were  prepared  by  Mme.  Curie 
in  Paris  and  by  Honigschmid  in  Vienna  from  which  secondary 
standards  ^^  have  been  furnished  to  all  the  principal  countries 
for  the  standardization  of  radium  by  means  of  its  y  radiation. 
That  quantity  of  any  other  member  of  the  uranium  family  in 
equilibrium  with  one  gram  of  radium  has  been  called  the  curie, 
a  unit  which  has  come  into  universal  use  for  radium  emanation, 
and  which  has  been  subdivided  into  milli-  and  micro-curies,  sig- 
nifying the  thousandth  and  millionth  parts,  respectively. 

9.    Kinetic  Energy  of  a  Particles. 

Since  all  a  particles  are  doubly  charged  helium  atoms  it  is 
evident  that  those  from  the  different  radioactive  substances  can 
differ  from  each  other  only  in  the  initial  velocity  with  which 
they  are  emitted;  and  that  furthermore,  when  one  a  particle  has 
lost  velocity  until  it  has  just  become  equal  in  velocity  to  one 
emitted  at  a  lower  value,  from  that  point  on  the  two  will  have 
identical  properties  in  the  same  medium.  These  statements 
have  been  fully  proved  by  W.  H.  Bragg  ^^  who  has  also  shown 
that  all  the  a  particles  emitted  by  the  same  kind  of  radioactive 
substance  have  the  same  initial  velocity,  which  means  that  they 
are  possessed  of  the  same  kinetic  energy  and  in  the  same  medium 
will  have  the  same  penetrating  power  and  other  properties  identi- 
cal. 

"Meyer  and  v.  Schweidler,  "RadioaktivitUt"   (191C),  p.  210. 

'"W.  H.  Bragg,  "Studies  In  Radioactivity"  (1912);  Bragg  and  Kleeman, 
PMl.  Mag.  (6)  10,  318-40;  11,  4GG-84  ;  W.  H.  Bragg,  ibid.,  11,  G17-32  ;  13,  507- 
16  ;  14,  425. 


BRIEF  OUTLINE  OF  RADIOACTIVITY  27 

10.  Range  of  a  Particles. 

The  distance  which  an  a  particle  can  penetrate  in  a  given 
medium  before  its  kinetic  energy  is  dissipated  is  called  its  range. 
The  range  usually  refers  to  a  gaseous  medium,  but  the  same 
term  is  used  for  penetration  in  liquids  or  solids.  It  is  believed 
that  at  the  end  of  its  range,  as  observed  by  the  cessation  of 
gaseous  ionization,  the  kinetic  energy  of  an  a  particle  is  re- 
duced practically  to  zero,  though  there  has  been  some  question 
on  this  point.  It  has  been  shown  by  Duane  ^*  that  the  a  particle 
loses  its  ability  to  produce  ionization,  luminescence  and  cliemical 
action  simultaneously.  Either  ionization  or  luminescence  may 
be  used  to  determine  the  range,  preferably  the  former.      \ 

The  following  Table  I  shows  the  members  of  the  uranium- 
radium  family  in  the  order  of  their  sequence,  indicates  the  kind 
of  radiation  accompanying  each  transformation  and  its  half  pe- 
riod; and  for  a  particles  shows  the  range  in  air  at  15°  ajad  760 
mms.,  the  initial  velocity,  and  the  total  number  of  pairs  of  ions 
produced  by  a  single  a  particle  in  its  whole  range.  ? 

11.  Ionizing  Power  of  a  Particles.  I 

An  a  particle  projected  from  an  atom  with  enormous  yelocity 
travels  in  a  straight  line  penetrating  all  the  atoms  encountered 
in  its  path.  By  penetration  is  meant  that  the  a  particle  passes 
through  the  electrical  field  due  to  the  electrons  surrounding 
the  atomic  nucleus  of  positive  charge,  as  conceived  in  the  Ruther- 
ford-Bohr ^^  atomic  model.  According  to  Rutherford's  idea,  re- 
sulting from  the  study  of  the  deflections  of  a  particles  near  the 
end  of  their  paths,  an  atom  consists  of  a  very  small  positive 
nucleus  with  an  elemental  charge  a  little  less  than  one-half  the 
atomic  weight,  surrounded  by  electrons  equal  in  number  to  the 
positive  nuclear  charge,  situated  in  rings  at  relatively  great  dis- 
tance from  the  positive  nucleus.  According  to  this  idea  of 
atomic  structure  which  has  now  become  generally  accepted,  it 
is  evident  that  an  a  particle  may  pass  through  a  large  number 
of  atoms  without  ever  coming  close  enough  to  the  nucleus  to 
have  its  course  altered,  as  long  as  its  velocity  is  great. 

^MVm.   Duane,  Comp.  rend.,  11,6,  958-60    (1908). 

'Mtutherfoid.  Nature,  92,  423  (1914);  Phil.  Mag.  (6)  27,  488-98  (1914). 
N.  Bohr,  Phil.  Mag.    (6)     20,   1-25;  47G-502 ;  857-75    (1913). 


28 


THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 


O 
so 

g 

CDs 

so 


I 

I 


•i 

I 


OS 

£  ^ 

'cd  •'^ 

P       •       •    CO    00 

to    05    TJH        •    t^       .       •       •    O       . 

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(N    :    :  c*^  CO 

'*.  CO  00     :  CO     •     •     •  CO     . 

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rH        •        .    ,-1    T-I 

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C3 
PL, 

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t^        .        .    T^    CO 

CO    (M    05       •    <N       •       •       '00       • 

it.  V 
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CO      t      t   ^,   tH 

tH        •        •    r-l    r-i 

lO    CO    CO        ;    05        I        ;        •.    lO        • 

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P^ 

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P^ 

S  an-cd:  »    « 

P^ 

OQ 

Half 
Period 

05       03     w     ?^    CO 

2  '^  a  s  ^ 

580  yrs. 
.85  days 
.05  min. 
6.8  min. 
9.6  min. 
0-«  sec. 
6  yrs. 
.85  days 
36  days 

oo 

^  CO  ^  ^  o 

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(N    (N    (M    (N    (N 

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M        l-H         hH        S 

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CZ2   *^ 

o3o3o3o3,j3c3c3c3c3c3 

r— 1 

Cr!cr!cnp^fr:piP:^P4p4« 

BRIEF  OUTLINE  OF  RADIOACTIVITY  29 

As  may  be  seen  in  Table  I,  a  single  a  particle  from  Ra  C 
produces  in  its  entire  path  in  air  237,000  pairs  of  ions,  which 
means  that  it  detaches  this  many  electrons  from  the  atoms  en- 
ct)untered.  Using  his  classical  oil  droplet  method,  Millikan^^ 
has  recently  shown  for  several  of  the  common  gases,  including 
air,  that  only  one  electron  is  detached  by  an  a  particle  from 
each  molecule,  leaving  a  singly  positively  charged  residual  mole- 
cule or  ion.  This  process  of  ionizing  requires  a  certain  expendi- 
ture of  energy  which  continues  to  lower  the  kinetic  energy  of 
the  a  particle  by  reducing  its  velocity  until  it  is  no  longer  able 
to  produce  ionization,  which  marks  the  end  of  its  range.  Unless 
acted  on  by  an  external  electrical  field  the  positive  and  negative 
ions  thus  separated  would  recombine  and  the  net  result  of  the 
expenditure  of  energy  would  be  the  production  of  heat  (assum- 
ing that  no  permanent  chemical  action  has  resulted) ;  or  in- 
versely, the  heat  evolution  of  radioactive  substances  emitting 
a  particles  is  a  measure  of  the  total  energy  available  for  ioniza- 
tion. From  a  knowledge  of  the  total  number  of  ions,  the  energy 
necessary  to  produce  one  pair  of  ions  in  air  has  been  calculated 
to  be  5.5x10"^^  ergs.^'^ 

The  property  of  producing  ionization  not  only  constitutes 
the  most  delicate  test  for  radioactive  substances  but  also  forms 
the  basis  of  their  quantitative  measurement.  Furthermore,  as 
will  be  shown  in  Chapter  VII,  the  relation  between  the  ioniza- 
tion and  the  chemical  effects  of  the  radiation  is  in  many  cases 
of  importance.  In  radiochemistry  one  is  interested  not  only  in 
the  total  ionization  produced  by  an  a  particle  but  also  in  the 
distribution  of  the  ionization  along  the  path  of  the  particle. 
This  subject  has  been  carefully  investigated  by  Bragg,  Geiger 
and  others.^^  Fig.  1  represents  the  ionization  curve  for  a  single 
a  particle  from  Ra  C  in  air,  in  which  the  length  of  path  is  plotted 
as  abscissae  and  the  number  of  ions  (pairs)  as  ordinates. 

The  form  of  the  curve  shows  that  for  the  first  two  or  three 
centimeters  of  path  the  ionization  remains  practically  constant 
at  about  2.2x10*  pairs  of  ions  per  cm.  of  path  traversed.  The 
number  then  begins  to  rise  and  increases  quite  rapidly  toward 

"R.  A.  Millikac,  V.  H.  Gottschalk,  M.  J.  Kelly,  Phys.  Rev.  (2)  15,  157-77 
(1920). 

"  Rutherford,   "Radioactive  Substances  and  Their  Radiations,"  p.  159. 

"W.  II.  Bragg,  "Studies  in  Radioactivity,"  Chapters  3  and  4.  H.  Geiger, 
Proc.  Roy.  Soc,  82,  489   (1909). 


30.      THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

8 


U 

o 

o 

BC 

w  4 

z 
o 


CO 


2  3  4  5  6 

RANGE  IN  CENTmETEf?SOF  AIR 

Fig.  1. 


the  end  of  the  range  and  then  drops  almost  abruptly  to  zero. 
The  total  number  of  ions  produced  in  the  whole  course  is  evi- 
dently represented  by  the  area  within  the  curve.  Since  a  par- 
ticles from  any  other  source  are  identical  except  in  initial  veloc- 
ity, their  ionization  curves  would  be  identical  after  any  point  at 
which  they  attain  the  same  velocity  as  that  represented  on  the 
curve  for  Ra  C.  For  example,  the  curve  for  Ra  A  would  be 
represented  by  counting  backward  from  the  end  of  the  curve 
4.7S  cms.,  the  length  of  the  range  of  the  a  rays  from  Ra  A. 
Similarly  if  either  end  of  the  path  of  an  a  particle  is  incomplete 
through  the  interposition  of  a  partial  screen,  or  if  the  ray  is 
absorbed  in  another  medium  before  completing  its  course,  the 
effective  ionization  may  still  be  obtained  by  referring  only  to 
the  effective  part  of  the  path. 


BRIEF  OUTLINE  OF  RADIOACTIVITY  31 

It  has  been  shown  by  Geiger  ^^  that  the  ionization  curve  for 
an  a  particle  corresponds  to  a  relation  between  the  velocity  (v) 
and  the  range  (R)  of  the  form:  v^  =  const.xR,  and  that  the 
ionization,  (I)  =  const.xR^/^,  from  which  it  follows  that  the 
total  ionization  of  a  single  a  particle  (k)  =  koR^/^,  in  which 
ko  is  a  constant  with  the  value  6.76x10*. 

12.    Enumeration  of  a  Particles. 

From  what  has  been  said  in  the  foregoing  paragraphs  it  is 
evident  that  the  counting  of  the  number  of  a  particles  emitted 
per  unit  time  by  any  given  radioactive  substance  is  very  impor- 
tant. Since  the  number  being  emitted  from  an  active  substance 
like  radium  is  very  large  (3.72x10^^  per  gram  per  second),  it  is 
necessary  to  reduce  both  the  quantity  of  substance  and  the  solid 
angle  from  which  the  effective  radiation  is  received.  Two  meth- 
ods of  detecting  and  counting  the  particles  have  been  employed: 
(1)  by  observation  of  the  number  of  scintillations  produced  on 
a  phosphorescent  ZnS  screen  under  low  magnification,  each 
spark  corresponding  to  the  impact  of  one  particle;  (2)  by  ob- 
servation of  the  number  of  deflections  of  an  electrometer  in  se- 
ries with  a  condenser  in  which  the  a  particles  are  received. 
These  two  entirely  different  methods  have  given  concordant  re- 
sults for  the  value  for  radium.^°  From  the  statements  in  §  8  it 
is  clear  that  any  other  member  of  the  uranium-radium  series 
which  emits  a  particles  will  emit  this  same  number  per  second 
from  the  equilibrium  quantity.  For  example,  the  emission  from 
radium  in  equilibrium  with  emanation,  Ra  A  and  Ra  C  will  be 
four  times  the  number  per  gram  of  radium;  the  emission  from 
one  curie  of  emanation  in  equilibrium  with  Ra  A  and  Ra  G 
would  be  three  times  this  same  number.  While  the  number, 
thirty-seven  billion  helium  atoms,  ejected  per  second  from  one 
gram  of  radium,  appears  very  high,  it  should  be  remembered 
that  at  even  this  rate  of  decay,  the  half  period  of  radium  is  1580 
years,  accounted  for  by  the  tremendous  number  of  atoms  repre- 
sented in  one  gram  or  even  one  cubic  centimeter  of  a  gas,  which 
is  of  the  order  of  billions  of  billions. 

"H.  Geiger,  Proc.  Roy.  800.,  83A,  505  (1910). 
*»  Rutherford,  Phil.  Mag.    (6)     28,  320-7    (1914). 


32  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

13.    Some  Additional  Properties  of  a  Particles. 

The  great  kinetic  energy  possessed  by  an  a  particle  com- 
pared with  that  of  even  the  swiftest  p  particle  (roughly  100 
times  as  great)  is  due  to  the  large  mass  of  the  former,  approxi- 
mately 7,000  times  that  of  an  electron.  The  a  particle  collides 
with  a  large  number  of  molecules  in  a  short  path,  thus  limiting 
its  total  penetrating  power  in  spite  of  its  great  momentum. 
Hence  a  particles  must  be  classed  as  non-penetrating  radiation. 
As  may  be  seen  in  Table  I,  they  have  ranges  in  air  at  ordinary 
pressure  of  3  to  8  cms.,  and  penetrate  other  substances  in  the 
inverse  order  of  the  "stopping  power"  of  the  given  substance. 

Stopping  Power.  The  term  stopping  power  of  a  substance, 
referring  to  its  power  to  stop  a  particles,  was  first  introduced  by 
Bragg.2^  Proceeding  from  the  generalization  that  the  a  ioniza- 
tion curves  of  different  gases  differ  from  each  other  only  in  a 
shortening  or  lengthening  of  all  the  ordinates  or  abscissae  by  the 
same  ratio,  the  following  very  simple  procedure  was  proposed  by 
Bragg.  Instead  of  having  to  determine  the  complete  curve  of 
ionization  for  each  gas  it  is  only  necessary  to  find  the  ioniza- 
tion, I,  at  one  particular  point,  R,  in  the  path  of  an  a  particle.  If 
I'  and  R'  are  the  corresponding  values  for  air,  the  ratio  of  the 
.total  ionization  (k)  in  the  two  media  may  then  be  expressed  by 
•RI/R'I'=k/k'(l) ;  and  putting  k',  the  total  ionization  for  air 
equal  to  1,  the  total  ionization  of  any  gas  is  referred  to  that  in 
air  and  may  be  called  the  total  specific  ionization.  But  if  it  is 
desired  to  refer  not  to  the  total  ionization,  but  to  that  produced 
along  a  certain  length  of  path,  which  is  evidently  equivalent  to 
referring  to  the  relative  ionization  in  a  single  molecule  of  each 
gas,  or  in  any  equal  number  of  molecules  of  each  gas,  one  must 
use  the  ratio  I/I',  which  can  be  shown  to  be  equal  to  Bragg's 
ks,  in  which  s  is  the  stopping  power,  as  follows:  Putting  the 
reciprocals  of  the  ranges  R  and  R'  equal  to  s  and  s',  the  respec- 
tive stopping  powers,  and  substituting  in  equation  (1)  above: 
I/I'=ks/k's'=ks,  by  putting  k's'  for  air  equal  to  1.  This  value 
may  be  called  the  molecular  specific  ionization  (Bragg's  ks)  to 
distinguish  it  from  the  total  specific  ionization  (k) .  In  Table  II 
will  be  found  the  values  for  a  number  of  common  gases  and 
other  substances  taken  from  Bragg.^^ 

a»W.  H.  Bragg,  "Studies  in  Radioactivity,"  Chapters  5  and  6  (1912). 
^rbid.  p.  65  (1912). 


BRIEF  OUTLINE  OF  RADIOACTIVITY 


33 


TABLE  II 

Stopping  Power  and  Ionization  (by  a  Rays)  of  Different  Gases 
According  to  Bragg 


k  X  100 

s  X  100 

ks  X  100 

Air 

100 

100 

100 

H, 

100 

24 

23.3 

N3 

96 

98.9 

94 

0. 

113 

106.4 

109 

CO 

101.5 

98.5 

100 

NO 

.... 

.... 

128 

CO3 

103 

150.5 

152 

N,0 

105  (99) 

146 

153 

NH3 

90 

81 

CS2 

137 

218* 

299 

SO2 

103 

201 

He 

.... 

2o!i 

21.1 

Ar 

•  • . . 

95.1 

124.5 

Br 

390 

HBr 

129* 



HI 

129 





HCl 

129 

. . . 



CH4 

118 

86 

110* 

CH4O 

122 

, . . , 

174 

C,H3 

126 

112 

140 

C,H, 

122 

135 

165 

C^He 

130 

151.4 

197 

C5H12 

135 

354.4 

485 

C^HeO 

123 

200 

246 

C.H, 

129 

333 

430 

CH3I 

133 

258 

343 

C,H,I 

128 

312 

400 

CHCI3 

129 

316 

408 

CCl, 

132 

400 

528 

CH3Br 

132 

203 

275 

Stopping  Power  (s) ;  Total  Ionization  (k) ;  and  Molecular 
Ionization  (ks). 

Bragg's  generalization  in  regard  to  stopping  power  does  not 
hold  strictly  for  different  substances  but  approximates  closely 
enough  to  be  of  service  for  all  practical  purposes  in  radio- 
chemistry. 

It  will  also  be  of  general  interest  to  note  that  the  study  of 
the  stopping  power  of  different  substances  for  a  particles  is  not 


34  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

confined  to  gases.  By  the  use  of  very  thin  sheets  as  screens  the 
stopping  power  of  the  heaviest  metals  has  been  determined  and 
may  be  translated  into  terms  of  air  equivalent.  Bragg  and  his 
co-workers  Have  found  (loc.  cit.)  that  the  stopping  powers  of 
the  various  metals  are  proportional  to  the  square  roots  of  their 
atomic  weights.  The  same  relationship  holds  approximately 
even  for  gases  as  light  as  air  and  hydrogen.  Bragg  has  also 
found  the  stopping  power  to  be  an  atomic  property  which  is 
additive  in  the  compounds  of  the  elements.  The  same  does  not 
hold,  however,  for  specific  ionization,  which  is  by  no  means 
additive  for  compounds.  This  must  mean  that  the  manner  in 
which  the  atoms  are  held  together  has  an  influence  on  the  ease 
with  which  electrons  can  be  detached,  and  since  it  is  now  gen- 
erally agreed,  that  the  atoms  are  held  together  by  means  of  the 
electrons,  this  reasoning  appears  all  the  more  plausible.  From 
Table  II  it  can  be  observed  that  as  the  molecular  weight  of 
chemical  substances  increases,  the  easier  it  becomes  for  a  par- 
ticles to  produce  ionization  in  them. 


14.    Characteristics   of  Members   of  the  Radium  Family  as 
Sources  of  Radiation. 

Up  to  the  present  only  members  of  the  radium  series  have 
been  used  quantitatively  in  studying  radiochemical  effects.  The 
members  preceding  radium  in  the  series  are  all  so  weakly  active 
that  they  do  not  come  into  consideration  as  artificial  means  of 
investigating  radiochemical  effects,  but  in  nature  they  play  a 
role  which  will  be  given  special  attention  in  some  of  the  later 
chapters  of  this  work.  This  statement  as  to  the  effects  in  nature 
would  apply  equally  well  to  the  members  of  the  other  radio- 
active families. 

Radium  itself  has  no  general  applicability  except  in  equilib- 
rium with  its  products  through  Ra  C,  which  necessitates  its 
being  maintained  in  a  sealed  container  on  account  of  the  gaseous 
nature  of  radium  emanation.  Owing  to  the  non-penetrating  char- 
acter of  a  rays,  only  (3  and  y  radiation  would  be  obtained 
through  the  walls  of  the  container.  Radium  salts  sealed  in  glass 
tubes,  therefore,  constitute  the  most  convenient  source  of  pene- 
trating rays,  having  the  advantage  of  constancy  of  radiation 
after  the  first  month  subsequent  to  sealing,  but  the  disadvantage 


I 


SRlEP  OUTLINE  OP  RADIOACTIVITY  35 

that  it  is  usually  difficult  to  determine  what  part  of  the  radia- 
tion is  effective  in  a  given  absorbing  system  under  working  con- 
ditions. Radium  in  equilibrium  with  Ra  C  has  four  sets  of  a 
particles,  one  each  for  Ra,  Ra  Em,  Ra  A,  and  Ra  C.  (See  also 
§  8.)      ^ 

Radium  Emanation  represents  one  of  the  most  convenient  and 
most  used  sources  of  radiation.  It  can  be  handled  as  a  gas,  can 
be  measured  with  ease,  and  can  be  introduced  into  the  interior 
of  many  systems  in  very  small  volume.  The  volume  of  1  curie 
of  emanation  (the  quantity  in  equilibrium  with  1  gm.  of  Radium) 
is  only  0.58  mm.^  and  furnishes  a  very  concentrated  form  of  ra- 
diation. It  does  not,  unlike  radium  salts,  appreciably  absorb 
its  own  radiations.  On  account  of  its  relatively  short  life,  it  has 
no  permanent  value  and  can  therefore  be  subjected  to  danger 
of  loss,  breakage,  etc.,  in  ways  that  would  not  be  feasible  with 
radium  salts.  Practically  its  only  disadvantage  consists  in  its 
short  life  and  continually  changing  activity,  but  since  this  change 
takes  place  according  to  a  perfectly  well  established  and  in- 
variable law,  it  can  readily  be  taken  into  account.  Its  radiations 
include  those  of  Ra  A,  Ra  B,  and  Ra  C,  with  which  it  attains 
equilibrium  after  four  hours  in  a  closed  vessel. 

Active  Deposit.  Ra  A,  Ra  B,  and  Ra  C  together  constitute 
the  so-called  active  deposit  of  radium  emanation  formerly  called 
also  "induced  activity,"  because  they  are  deposited  as  solids  on 
the  walls  of  a  containing  vessel  or  on  any  surrounding  objects 
to  which  the  emanation  may  diffuse  and  owing  to  their  activity 
appear  to  impart  to  these  objects  a  temporary  radioactivity. 
Ra  A  emits  only  a  rays,  Ra  B  only  rather  non-penetrating  |3  and 
Y  rays.  On  account  of  the  extremely  short  life  of  Ra  C 
(10-®  sec),  both  Ra  C^  and  Ra  C  will  be,  in  the  following 
pages,  referred  to  collectively  as  Ra  C,  which  then  constitutes 
not  only  a  source  of  a  rays,  but  also  of  the  most  penetrating 
P  and  Y  rays  in  the  radium  series.  The  y  rays  of  Ra  C  furnish 
the  best  means  of  measuring  either  radium  or  radium  emanation. 

Radium  D  and  E  possess  no  rays  of  radiochemical  impor- 
tance. Ra  F  (polonium)  is  unique  in  furnishing  only  a  rays 
and  is  the  most  convenient  source  of  this  form  of  radiation  free 
from  penetrating  rays.  It  is  usually  deposited  electrolytically 
on  copper,  which  then,  of  course,  absorbs  that  half  of  the  a  radia- 


36      THE  CHEMICAL  EFPECtS  OP  ALPHA  PARTICLES  AlfD  EtECfROm 

tion  directed  toward  it.     Especially  for  use  in  liquid  systems, 
polonium  is  a  very  suitable  source  of  a  rays. 

As  generally  applicable  to  all  a  particles,  it  should  be  men- 
tioned that  Rutherford  and  Geiger  ^^  utilized  the  a  radiation 
from  polonium  to  determine  the  probability  variations  of  the 
emissions  of  a  rays  both  with  respect  to  time  and  space  and 
found  their  distribution  fully  obeying  the  laws  of  chance. 

a» Rutherford  and  Geiger,  Phil.  Mag.   (6)    20,  698-704   (1910). 


Chapter  3. 
Electrical  Effects — Ionization. 

15.    Saturation  Current  as  a  Measure  of  Ionization. 

The  general  principle  of  the  method  of  the  measurement  of 
gaseous  ionization  deserves  at  least  brief  consideration.  Let  us 
suppose  that  the  air  in  a  closed  chamber  provided  with  electrodes 
is  subjected  to  a  constant  radiation  that  will  produce  a  fixed 
number  of  ions  in  the  chamber  in  unit  time.  Connect  the  elec- 
trode terminals,  which  must  be  carefully  insulated  from  the 
chamber  and  from  the  surrounding  air,  in  series  with  an  instru- 
ment capable  of  measuring  low  electrical  current,  such  as  a 
quadrant  electrometer.  Apply  from  a  high  voltage  battery  suc- 
cessively increasing  voltages  and  plot  a  current-voltage  curve  as 
in  Fig.  2.  For  low  voltages  the  curve  rises  linearly,  indicating 
that  the  current  increases  in  direct  proportion  to  the  applied 
voltage  just  as  would  be  required  by  Ohm's  law  in  a  conductor 
of  the  first  class.  On  applying  yet  higher  voltage  the  current 
rises  more  slowly  than  the  voltage  and  finally  reaches  a  constant 
maximum  in  the  part  of  the  curve  AB  (Fig.  2)  which  remains 
horizontal.  It  can  now  be  inferred  that  all  the  available  ions  are 
being  drawn  to  the  electrodes  and  are  discharged,  and  that  fur- 
ther increase  of  voltage  within  suitable  limits  produces  no  in- 
crease of  current.  This  current  is  designated  as  saturation  cur- 
rent, which  is  evidently  a  direct  measure  of  the  total  number  of 
ions  being  formed  per  unit  time  in  the  chamber.  It  is  also  in- 
ferred that  under  conditions  in  which  insufficient  voltage  is  ap- 
plied the  ions  not  attracted  to  the  electrodes  recombine  with  each 
other  by  ordinary  diffusion. 

The  potential  that  must  be  applied  to  produce  saturation  cur- 
rent will  depend  on  the  strength  of  the  ionization  and  the  gaseous 
pressure,  the  lower  the  pressure  the  smaller  the  required  volt- 
age. At  atmospheric  pressure  2,000-5,000  volts  per  cm.  will  suf- 
fice in  most  cases.  However,  if  the  ionization  is  very  great,  such 
as  that  produced  by  a  strong  a  ray  source,  it  becomes  impossible 

37 


38  THE  CHEMICAL  EFFECTS  O^  ALPHA  PARTICLES  AND  ELECTRONS 

to  produce  saturation  current.  The  measurement  even  of  mod- 
erate ionization  produced  by  a  rays  has  been  found  to  present 
especial  difficulties,  supposedly  due  to  the  high  concentration  of 
ions  along  the  path  of  the  particle.  One  is  seldom  able  to  meas- 
ure directly  the  ionization  of  a  rays  of  an  intensity  suitable  for 


the  measurement  of  its  chemical  action  also,  and  must  resort  to 
indirect  methods  of  calculating  the  ionization  which  will  be 
treated  in  Chapter  VII.^  * 

*  In  connection  with  tlie  mcasurcmont  of  gaseous  ionization  by  moans  of 
saturation  current,  it  sliould  be  pointed  out  tbat  while  the  practice  among 
physicists  of  referring  to  the  total  number  of  pairs  of  ions  is  fairly  common, 
the  expression  ions  where  pairs  of  ions  is  meant  is  also  unfortunately  preva- 
lent. This  is  particularly  confusing  to  the  chemist,  who  in  dealing  with  electro- 
lytic ions  in  connection  with  the  solution  tlieories,  always  means  total  positive 
and  negative  ions,  never  ions  of  only  one  sign.  Naturally  the  physicist  in  tak- 
ing current  units  as  the  measure  of  gaseous  ionization  is  prone  to  neglect  the 
other  half  of  the  ionization,  thus  leading  to  confusion  in  cases  where  the  number 
of  ions  of  both  signs  is  important. 


ELECTRICAL  EFFECTS— IONIZATION  39 

16.    Ionization  by  Electronic  Shock. 

To  return  to  the  curve  in  Fig.  2,  if  the  voltage  be  increased 
beyond  that  necessary  for  saturation  current,  the  electrons  and 
ions  attain  still  greater  velocities,  and  soon  the  electrons  reach 
velocities  within  their  free  paths,  at  which  their  kinetic  energy 
becomes  sufficient  to  ionize  the  gas  molecules  with  which  they 
come  in  contact,  thus  increasing  the  total  number  of  electrical 
carriers  beyond  the  number  being  produced  by  primary  radiation. 
Owing  to  the  rapid  increase  in  the  number  of  carriers  the  cur- 
rent again  begins  to  rise,  as  indicated  by  the  curve  BC,  on  ac- 
count of  this  process  which  has  been  called  ionization  by  "shock" 
or  collision. 

As  will  be  later  shown  (§  52)  this  form  of  ionization  prob- 
ably plays  a  very  important  part  in  the  chemical  action  pro- 
duced by  electrical  discharge  through  gases.  Evidently  there 
is  no  limit  to  the  current  resulting  from  such  an  increase  in 
voltage  until  the  sparking  potential  is  reached.  The  current 
resulting  from  ionization  by  shock  usually  will  not  represent 
a  condition  of  saturation.  At  ordinary  gas  pressures,  only  a 
small  fraction  of  the  total  number  of  ions  produced  by  an  in- 
tense discharge  reaches  the  electrodes  before  recombining,  and  it 
is  only  this  small  fraction,  of  course,  which  carries  the  current; 
the  other  ions  may  recombine  to  form  the  original  product,  or 
may  combine  to  form  a  new  chemical  product,  hence  their  interest 
in  radiochemistry. 

X  ray  Tubes  may  be  very  aptly  employed  to  illustrate  ioni- 
zation by  shock.  The  old  ordinary  form  of  X  ray  tube  depends 
upon  shock  ionization  for  a  sufficient  number  of  carriers  to  con- 
duct the  current,  which  explains  why  the  gas  pressure  had  to  be 
held  within  rather  narrow  limits;  if  too  high,  the  free  path  of 
the  electrons  was  too  short  to  enable  them  to  obtain  the  neces- 
sary velocity  to  produce  ionization  by  shock;  if  too  low,  not 
enough  encounters  resulted  to  maintain  discharge.  The  ordi- 
nary X  ray  tube  has  a  well  known  tendency  to  become  "hard" 
by  reduction  of  the  gas  pressure,  which  is  also  a  result  of  ioniza- 
tion. It  means  that  some  of  the  positive  gas  ions  attain  a  ve- 
locity sufficient  to  cause  them  to  adhere  to  the  electrode  upon 
reaching  it,  thus  reducing  the  pressure.  Whether  the  effect  is 
chemical  or  physical  has  not  been  definitely  determined.     The 


40  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

same  general  type  of  "clean  up"  may  be  illustrated  by  passing 
a  discharge  through  radium  emanation  in  a  small  Geissler  tube. 
After  the  tube  has  operated  for  some  time  under  suitable  con- 
ditions, it  will  be  found  that  quite  a  fraction  of  the  gas  has 
been  driven  into  the  negative  electrode,  or  into  the  platinum  mir- 
ror immediately  surrounding  it,  so  that  it  can  not  be  pumped 
out.  The  exact  location  of  the  emanation  can  be  most  conven- 
iently found  by  dissecting  the  tube  and  examining  the  various 
parts  for  y  radiation. 

The  Coolidge  ^  X  ray  tube  does  not  depend  on  ionization  by 
shock,  but  on  the  direct  production  at  a  highly  heated  tungsten 
cathode  of  enough  therm-electrons  to  carry  the  current.  Conse- 
quently the  gas  pressure  in  a  Coolidge  tube  may  be  lowered  ad 
libitum,  which  gives  the  electrons  much  longer  free  paths,  result- 
ing in  their  arriving  at  the  target  with  very  high  velocity,  pro- 
ducing X  rays  of  much  shorter  wave  length  and  higher  pene- 
trating power.  It  has  not  yet  been  possible  to  equal  y  rays  in 
these  respects. 

17.    Some  Properties  of  p  Particles  and  Electrons. 

P  particles  are  electrons  emitted  from  radioactive  substances. 
They  differ  very  markedly  from  a  particles  in  many  respects. 
Their  much  smaller  mass  prevents  their  carrying  the  same  order 
of  kinetic  energy  even  when  moving  at  velocities  approaching 
that  of  light.  The  initial  velocities  of  the  various  p  particles 
vary  from  0.3  to  0.98  of  the  velocity  of  light.  Like  a  particles 
they  produce  ionization  and  phosphorescent  and  photographic 
as  well  as  chemical  effects.  The  electrical  method  presents  the 
best  means  for  their  study.  The  idea  that  formerly  prevailed 
that  each  radioactive  substance  emits  only  a  single  simple  type 
of  p  radiation  has  had  to  be  abandoned  in  favor  of  the  view  that 
great  variations  exist  with  respect  to  velocity  of  emission. 
Coupled  with  the  fact  that  their  ionizing  and  penetrating 
properties  are  highly  dependent  upon  velocity,  a  degree  of  com- 
plexity and  uncertainty  is  encountered  in  dealing  with  p  par- 
ticles which  is  quite  foreign  to  the  exact  nature  of  our  knowl- 
edge regarding  a  particles.    The  apparent  mass  of  the  electron 

»W.  D.  Coolldgo,  Phys.  Rev.   (2)   2,  409-30   (1914). 


tJLECtRICAL  EFFECTS— lONIZAf ion  41 

has  also  been  found  to  vary  with  its  velocity.  Kaufmann^ 
has  made  the  most  exact  investigation  of  this  subject. 

The  absorption  phenomena  for  p  rays  are  also  very  different 
from  those  for  a  rays.  It  has  already  been  pointed  out  that  the 
cc  particle,  while  non-penetrating  to  collective  matter  owing  to 
the  large  number  of  collisions  made  in  a  short  path,  is  extremely 
penetrating  with  reference  to  the  individual  atom,  traveling  in 
a  straight  line  through  an  immense  number  before  its  energy 
is  expended.  For  p  particles  exactly  the  opposite  is  true.  To 
matter  collectively  they  are  quite  penetrating,  because  owing  to 
their  small  size  and  high  velocity  they  "slip  between"  the  mole- 
cules, making  a  much  smaller  number  of  collisions  per  unit 
path,  but  suffer  a  much  greater  deflection  or  scattering  for  each 
collision.  Consequently  the  paths  by  which  p  particles  traverse 
matter  ate  very  far  from  straight  lines;  they  are  even  frequently 
deflected  through  180°  and  return  in  the  opposite  direction. 
This  ease  of  deflection  corresponds  to  the  well  known  ease  with 
which  they  are  deflected  by  electrical  and  magnetic  fields.  Be- 
sides the  gradual  reduction  in  velocity  experienced  by  p  rays 
similar  to  that  of  a  rays,  it  is  also  probable  that  at  any  part  of 
its  course  a  P  ray  may  collide  with  a  molecule  in  such  a  way  that 
it  is  stopped  abruptly.  This  means  that  instead  of  all  p  rays 
with  a  given  initial  velocity  traveling  the  same  distance  in  an 
absorbing  medium,  as  do  a  rays,  they  are  gradually  absorbed 
proportionally  to  the  number  remaining  to  be  absorbed  at  any 
point  in  the  path,  which  behavior  would  be  expressed  by  an 
exponential  law.  Owing,  however,  to  the  various  complications 
which  arise  through  scattering,  unequal  velocities  and  other 
causes,  the  direct  application  of  an  equation  of  the  form: 
I=Io(l-e-^^)  is  possible  only  in  a  few  special  cases,  lo  being  the 
initial  intensity,  and  I  that  after  the  radiation  has  traversed  the 
thickness  d  in  a  medium  with  an  absorption  coefficient  \i. 

Owing  to  its  smaller  mass  and  kinetic  energy,  a  p  particle 
produces  much  less  ionization  than  does  an  a  particle,  200  fold 
less  on  the  average  per  unit  path  for  p  particles  expelled  from 
radium.  The  total  number  of  p  particles  emitted  by  radioactive 
substances  is  not  known  with  the  same  degree  of  accuracy  as  in 
the  case  of  a  particles,  but  the  evidence  points  to  the  conclu- 
sion that  the  emission  of  one  p  particle  per  atom  decaying  is  the 

aw.  Kaufmann,  PJujs.  Zeit.,  4,  54   (1902). 


42  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

rule  for  elements  showing  p  radiation.  A  very  strong  piece  of  in- 
direct evidence  in  favor  of  this  view  is  the  principle  discovered 
and  elaborated  by  Russell,-*  Soddy,^  Fajans,^  v.  Hevesy/  and 
others,  according  to  which  an  element  emitting  a  particles  pro- 
duces an  element  possessing  chemical  valence  two  units  less  than, 
and  occupying  a  place  in  the  periodic  system  two  places  to  the 
left  of,  that  of  the  parent  element;  while  an  element  emitting  p 
radiation  produces  an  element  shifted  one  unit  in  the  opposite 
direction  with  respect  to  valence  and  position  in  the  periodic 
system.  These  relations  evidently  require  a  unit  relationship  be- 
tween the  number  of  atoms  changing  and  the  number  of  a  or  p 
particles  primarily  emitted.  Experimental  evidence  also  indicat- 
ing a  number  of  p  particles  of  that  order  was  obtained  by  Mose- 
ley  ®  and  more  recently  by  Hess  and  Lawson.^  The  total  num- 
ber of  ions  produced  in  air  by  the  p  rays  from  one 'gram  of 
radium  in  equilibrium  was  found  by  Moseley  and  Robinson  ^°  to 
be  about  9x10^*  per  second,  and  by  the  y  rays  13x10^*  per  sec- 
ond. Rutherford  ^^  estimates  for  radium  in  equilibrium  that  of 
the  total  radiated  energy,  3.2%  is  in  the  form  of  p  rays  and 
4.7%  in  the  form  of  y  rays,  the  balance  being  represented  by 
a  radiation. 

The  swiftest  p  rays  from  Ra  C  will  penetrate  in  air  about 
3  m.  but  are  entirely  stopped  by  2  mm.  of  lead.  Owing  to  their 
great  range  in  air  and  the  sparsity  of  the  ionization  along  their 
paths,  p  rays  can  not  be  utilized  very  effectively  to  produce 
radiochemical  actions  in  a  gaseous  system.  Their  greater  absorp- 
tion in  liquids  and  solids  is  more  favorable  for  chemical  effects. 

As  in  the  case  of  a  particles,  the  ionization  produced  in  gases 
by  P  and  y  rays  has  been  shown  by  Millikan  and  his  co- 
workers ^^  to  consist  in  the  detachment  of  one  electron  from  each 
molecule,  leaving  a  singly  charged  positive  ion. 

The  subject  of  the  production  of  ionization  by  electrons  has 

*A.  S.  Russell,  Clicm.  News,  107,  49-52   (1913). 

•F.  Soddy,  "Chemistry  of  the  Kadioelenients,"  Pt.  II,  pp.  16-20  (1914). 
•K.  Fajans,  Phya.  Zeit.,  14,  1.31  (1913)  ;  ibid.,  IG,  450  (1915). 
'v.  Hevesy,  ibid.,  14,  49   (1913). 

•H.  G.  J.  Moseley,  Proc.  Roy.  Soc,  87A,  230   (1912). 

•v.  F.  Hess  and  R.  W.  Lawson,  Sltb.  Vienna  Acad.  Ila,  125,  GG1-G74 
(1916). 

'«>H.  G.  J.   Moseley  and  IT.   Robinson,  Phil.  Mag.    (G)    2S,  327-37    (1914). 
"Rutherford,  "Radioactive  Substances,"  pp.  579-80   (1913). 
"R.  A.  Millilian  and  II.  Fletcher,  Phil.  Mag.  (G)   21,  753  (1911). 


ELECTRICAL  EFFECTS— IONIZATION  43 

already  been  considered  in  its  qualitative  aspects  in  §  17.    The 

quantitative  relations  have  been  most  thoroughly  investigated  by 

Townsend  ^^  for  ionization  produced  by  electrons  of  photo-electric 

origin  accelerated  by  various  voltages  in  an  electrical  field  of 

definite  dimensions.    The  general  equation  of  Townsend  has  the 

Ho  (a 6)e(''— '^^'^ 

form:  n  =  ■ ^    {a-p)^      ^^  which  Uq  is  the  number  of  ions 

set  free  at  the  cathode,  n  is  the  initial  number  of  ions  reach- 
ing the  other  electrode  if  a  is  the  average  number  of  new  ions 
produced  per  cm.  by  each  negative  ion,  and  p  by  each  positive 
ion,  d  is  the  distance  between  the  electrodes,  with  the  potential 
X  and  the  gas  pressure  P  remaining  constant.  When  X/P  is 
small  the  ionization  produced  by  positive  ions  is  sensibly  zero 
and  the  equation  takes  the  simple  form :  n  =  UoCa'^.  More  re- 
cently Horton  ^*  has  proved  the  applicability  of  Townsend's 
equation  to  ^/lerm-electrons.  Townsend's  results  show  that  for 
a  pressure  of  1  mm.  of  air,  maximum  ionization  is  attained  by 
increase  of  voltage  when  the  ionization  reaches  a  value  of  about 
20  pairs  of  ions  per  1  cm.  of  path. 

Recently  many  investigations  have  been  made  to  determine 
the  minimum  voltage  at  which  radiation  and  ionization  effects 
begin  in  different  gases,  in  connection  with  the  application  of 
the  quantum  theory.  Consideration  of  these  results  is  outside 
the  scope  of  the  present  work. 

In  general  it  may  be  pointed  out  that  up  to  the  present, 
except  for  the  work  of  Kirkby  (see  §  52),  the  chemical  effects 
of  the  passage  of  electricity  through  gases  have  not  been  studied 
under  conditions  at  which  Townsend's  equations  would  be  ap- 
plicable, and  the  total  ionization  has,  therefore,  been  unknown. 
Comparison  of  the  amount  of  chemical  action  with  other  fac- 
tors such  as  current,  voltage,  ultra-violet  radiation,  etc.,  has  not 
proved  very  illuminating.  It  is  to  be  hoped  that  future  work  will 
throw  more  light  upon  the  fundamental  relations  involved, 
through  a  study  of  the  chemical  effects  of  the  passage  of  elec- 
tricity through  gases  under  more  suitable  experimental  condi- 
tions. 

'3  J.  S.  Townsend,  PMl.  Mag.    (6)    1,   p.  198    (1901)  ;  iUa.,  3,  557   (1902)  ; 
"Theory  and  Ionization  of  Gases  by  Collision"    (1910). 
i*F.  Horton,  Phil.  Mag.    (6)    34,  461-78    (1917), 


44  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

18.    Y  Rays  and  X  Rays. 

The  announcement  by  Roentgen  in  1895  of  the  discovery  of 
the  so-called  X  or  Roentgen  rays  marked  the  beginning  of  a 
new  era  in  the  progress  of  science.  Almost  immediately  it  led 
to  the  discovery  by  Becquerel  of  the  radioactive  radiations, 
which  was  followed  but  little  later  by  the  discovery  of  radium  by 
the  Curies,  and  by  the  rapid  development  of  the  subject  of 
radioactivity  by  Rutherford  and  Soddy  and  a  host  of  others  too 
numerous  to  mention  here.    It  was  early  found  that  both  X  and 

Y  rays  possess  in  common  with  a  and  p  rays  the  power  of  ioniz- 
ing gases,  and  of  producing  photographic  and  phosphorescent  ef- 
fects. Unlike  the  two  latter,  X  and  y  rays  are  not  deviated  by 
electrical  nor  magnetic  fields,  do  not  carry  electrical  charge, 
and  are  possessed  of  unusual  penetrating  powers,  in  which  the 

Y  rays  far  exceed  the  X  rays. 

The  electro-magnetic  nature  of  X  rays  was  recognized  quite 
early  and  they  were  classified  as  ether  pulses  of  short  wave 
length  having,  naturally,  the  same  velocity  as  light.  Although 
the  general  similarity  between  X  and  y  rays  was  evident  from 
the  first,  it  was  not  until  much  later  that  it  was  possible  to 
demonstrate  clearly  that  y  rays  are  also  ether  pulses  having  yet 
greater  frequency  and  correspondingly  shorter  wave  lengths  than 
X  rays. 

Not  only  did  the  discovery  of  X  and  y  rays  play  an  important 
part  in  the  initiation  of  the  new  development  in  physics  and 
chemistry,  but  their  further  investigation  has  proved  extremely 
fruitful  in  several  directions.  The  discovery  by  Laue  ^^  of  the 
interference  principle  for  X  rays  and  its  application  by  Friedrich, 
Knipping  and  Laue  ^®  to  the  use  of  crystals  as  three  dimensional 
diffraction  gratings  was  shortly  followed  by  the  brilliant  work 
of  W.  L.  Bragg  ^^  on  the  use  of  crystals  for  the  specular  reflec- 
tion of  X  rays,  which  resulted  in  investigations  of  fundamental 
importance  both  with  respect  to  crystal  structure  and  the  nature 
of  X  rays.^®    The  classical  discovery  by  Moseley  ^^  of  the  rela- 

"  M.  Laue,  Sitzb.  Akad.  Wiss.  Muenchen,  1912,  pp.  2G3-73. 

»«W.  Friedrich,  P.  Knipping,  and  M.  Laue,  ibid.,  1912,  pp.  303-22. 

I'W.  L.  Bragg,  "Nature,"  90,  410  (1912)  ;  Proc.  Camb.  Phil.  Soc,  17,  43- 
57  (1913). 

""X  Rays  and  Crystal  Structure,"  W.  H.  and  W.  L.  Bragg  (1915).  W.  L. 
Bragg,  Phil.  Mag.   (6)   40,  169-89   (1920). 

»H.  G.  J.  Moseley,  Phil.  Mag.   (G)   26,  1024-34  (1913)  ;  27,  703-13  (1914). 


ELECTRICAL  EFFECTS— IONIZATION  45 

tionship  between  the  X  ray  spectra  of  different  elements,  leading 
to  the  establishment  of  the  so-called  atomic  numbers,  has  opened 
the  way  to  substantial  progress  in  the  solution  of  the  problem 
of  atomic  structure.  The  work  of  Barkla,^*'  Darwin,  Sadler,  and 
later  of  Siegbahn,^!  Duane,^^  Hull,^^  and  others  on  the  various 
types  of  characteristic  radiations  from  the  elements  can  merely 
be  cited. 

Through  some  of  the  work  on  characteristic  radiations  just 
referred  to,  Rutherford  was  led  to  suspect  that  the  y  rays  may 
be  the  characteristic  radiation  excited  by  the  emission  of  p  rays. 
The  plausibility  of  this  hypothesis  has  been  supported  from  sev- 
eral different  points  of  view  until  no  doubt  remains  of  the  ex- 
istence of  this  relation  of  the  origin  of  y  rays  from  p  radiation. 
This  does  not  mean,  however,  that  a  single  p  ray  sets  up  a  single 
Y  ray  pulse.  As  was  seen  in  the  preceding  paragraph  the  total 
ionization  by  y  rays  from  radium  in  equilibrium  was  found  by 
Moseley  and  Robinson  (loc.  cit.)  to  be  of  the  order  13x10^*  pairs 
per  second,  about  50%  greater  than  that  from  the  total  p  radia- 
tion. 

The  most  penetrating  y  rays  traverse  several  centimeters  of 
lead  or  several  hundred  meters  of  air.  In  the  latter  part  of  the 
path  through  lead  the  absorption  becomes  exponential  in  char- 
acter. Owing  to  their  great  penetrating  powers  it  is  difficult  to 
utilize  Y  rays  efficiently  in  the  study  of  radiochemical  effects. 
The  subject  appears  to  have  great  importance,  however,  since 
it  has  been  found  that  it  is  the  physiological  effects  of  the  y  fo^ys 
which  are  utilized  therapeutically,  but  whether  or  not  the  ef- 
fect is  produced  through  the  intermediation  of  chemical  action  re- 
mains as  yet  wholly  unknown.  The  utilization  of  the  new  power- 
ful types  of  X  ray  tubes,  such  as  the  Coolidge  tube  (§  17), 
also  offers  an  attractive  future  field  for  the  investigation  of  radio- 
chemical effects. 

20  C.  G.  Barkla,  Phil.  Mag.   (6)   22,  396-412;  PTiys.  Zeit.,  15,  160   (1914). 

»Manne  Siegbahn,  Phys.  Zeit.,  15,  753-6  (1914)  ;  Verh.  deut.  phys.  Ges.  18,. 
150-3  (1916)  ;  Nature,  96,  676  (1916)  ;  Yerh.  deut.  phys.  Ges.  18,  278-82  (1916). 

"  Wm.  Duane  and  Kang-Fuh  Hu,  Phys.  Rev.  (2)  11,  489  (1918)  ;  Duane 
and  T.  Shimizu,  iMd.,  13,  306  (1919). 

2«A.  W.  Hull,  Am.  Joum.  Roentgenol.  2,  893  (1915)  ;  J.  Frank.  Inst.,  181, 
423. 


Chapter  4. 
Qualitative  Radiochemical  Effects. 

19.    General  Classification. 

The  observation  and  investigation  of  radiochemical  effects 
have  embraced  a  fairly  broad  field  with  rather  undefined  bound- 
aries. At  the  one  extreme  are  those  effects  of  radiation  which 
are  not  definitely  known  to  be  chemical  in  nature,  such  as  phos- 
phorescence, coloring,  and  thermoluminescence.  Their  quantita- 
tive aspects  from  the  chemical  standpoint  have  hardly  been 
touched  upon.  At  the  other  extreme  will  be  found  a  very  limited 
number  of  definite  chemical  reactions  which  have  been  found  to 
take  place  under  the  influence  of  a  radiation,  and  which  have 
been  very  thoroughly  investigated  both  with  respect  to  the  nature 
and  amount  of  the  chemical  action  produced,  and  also  with  re- 
spect to  the  amount  of  radiation  producing  it,  and  the  mode  of 
the  expenditure  of  the  radiant  energy  in  the  system  acted  on. 
Between  these  two  extremes  will  be  found  all  degrees  of  varia- 
tion with  respect  to  the  qualitative  or  quantitative  character  of 
the  'chemical  and  radiant  factors  involved  in  the  reactions 
studied. 

Radiochemical  investigations  may  be  arbitrarily  classified  as 
follows: 

(1)  Reactions  of  doubtful  chemical  nature  which  have  nbt 
yet  been  thoroughly  explained. 

(2)  Reactions  undoubtedly  chemical  in  nature  but  in  which 
the  exact  chemical  composition  of  some  of  the  products  has  not 
been  determined. 

(3)  Reactions,  the  chemical  products  of  which  have  been 
identified  but  not  quantitatively  measured. 

(4)  Reactions  in  which  the  products  have  been  identified 
and  measured  but  where  the  quantity  of  radiation  was  not 
known. 

(5)  Reactions  in  which  the  products  were  identified  and 

46 


QUALITATIVE  RADIOCHEMICAL  EFFECTS  47 

measured  and  the  total  quantity  of  radiation  was  known,  with- 
out being  able  to  determine  what  part  of  the  radiation  was 
effective  in  the  given  system. 

(6)  Reactions  characterized  by  (5)  with  the  additional 
knowledge  of  the  effective  radiation. 

(7)  Reactions  characterized  by  (6)  with  complete  informa- 
tion as  to  the  kinetics  of  the  reaction  from  the  physical-chemicaj 
standpoint. 

20.  Qualitative  Observations. 

The  observation  of  some  of  the  remarkable  chemical  effects 
of  the  rays  of  radium  followed  very  closely  upon  its  discovery. 
P.  and  Mme.  Curie  ^  in  1899  reported  the  coloration  of  glass 
and  of  porcelain,  as  well  as  the  formation  of  ozone  from  oxygen 
(observed  by  Demarcay).  F.  Giesel  ^  found  that  coloration  of 
the  alkaline  halides  was  produced  similar  to  that  by  cathode 
rays,  and  that  water  is  decomposed  into  its  elements.  Becquerel  ^ 
showed  that  the  p  and  y  rays  produce  many  of  the  reactions 
that  can  be  brought  about  by  the  action  of  light,  such  as  the 
change  of  white  to  red  phosphorus,  and  the  decomposition  of 
hydriodic  acid  solution  and  of  mercuric  chloride.  Jorissen  and 
Woudstra  *  showed  that  the  coagulation  of  some  colloidal  solu- 
tions is  caused-  by  the  penetrating  radium  rays.  Jorissen  and 
Ringer  °  demonstrated  the  combination  of  hydrogen  and  chlorine 
gases  at  ordinary  temperature  under  the  influence  of  the  pene- 
trating rays. 

21.  Coloration  and  Decomposition  of  Radium  Salts. 

Radium  salts  mixed  with  barium  salts  in  various  proportions 
undergo  spontaneous  alterations  which  are  first  marked  by  a 
change  of  color  from  the  original  pure  white  to  a  brownish  tint 
which  increases  in  depth  with  a  rapidity  dependent  upon  the 
quantity  of  radium  present.  This  progressive  change  in  color 
is  exhibited  very  strikingly  by  Ba(Ra)Br2;  if  successive  frac- 

ip.  and  M.  Curie,  Comp.  rend.  129,  823  (1899). 

2F.  Giesel,  Verh.  deut.  phija.  Gea.  2,  9  (1900). 

3  II.  Becquerel,  Comp.  rend.  133,  709-12  (1901). 

*  W,  P.  Jorissen  and  H.  W.  Woudstra,  Zeit.  Chem.  u.  Industrie  d.  Kolloide 
10,  280  (1912). 

"W.  P.  Jorissen  and  W.  E.  Ringer,  Ber.  38,  899  (1905)  ;  39,  2093  (1906)  ; 
Arch.  Ndcrland.  Sci.  Exact,  et  Nat.  (ii)  XII,  p.  157  (1907). 


48  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

tions  with  approximately  the  same  radium  content  are  crystal- 
lized daily,  it  is  possible  to  judge  their  relative  ages  during  the 
first  few  weeks  by  the  depth  of  color.  Honigschmid  ^  has  ob- 
served that  radium  salts  which  have  not  been  heated  above 
200°  C.  take  on  only  a  weak  yellowish  or  gray  color  even  after 
several  years,  while  those  which  are  heated  to  red  glow  become 
almost  black  in  one  or  two  days.  Since  he  found  the  drying  to 
be  complete  in  either  case  Hoenigschmid  did  not  attribute  the 
difference  to  traces  of  water  of  crystallization.  (Like  the  corre- 
sponding barium  salts,  both  RaBra  and  RaClg  crystallize  as 
RaBr2.2H20  and  RaCl2.2H20.)  Radium  chloride  undergoes  a 
similar  change  in  color,  which  does  not  appear  to  develop  so 
rapidly  as  in  the  case  of  the  bromide.  A  further  proof  of  the 
spontaneous  chemical  change  of  radium  salts  is  obtained  on  dis- 
solving them  in  water  after  they  have  been  stored  for  some  time. 
Solution  is  invariably  accompanied  by  a  more  or  less  copious 
evolution  of  gas.  On  dissolving  the  chloride  in  water  an  odor 
of  CI  and  CIO2  is  often  perceptible.  The  dry  salt  stored  in  a 
desiccator  also  has  the  odor  of  free  chlorine  and  of  ozone.  The 
nature  of  the  changes  produced  in  the  salt  itself  has  not  been 
thoroughly  investigated,  but  it  is  probable  that  the  larger  part 
of  the  gas  evolution  observed  on  dissolving  is  due  to  the  release 
of  some  hydrogen  (and  oxygen)  produced  by  the  radiochemical 
decomposition  of  remaining  traces  of  water.  In  containers  filled 
with  air  part  of  the  salt  is  also  doubtless  converted  into  oxy- 
halide,  oxide,  and  even  some  carbonate. 

It  has  been  shown  by  P.  Curie  and  Debierne '  that  a  vacuum 
can  not  be  maintained  over  the  solid  salts,  and  that  from  a  solu- 
tion of  radium  salts  a  continuous  evolution  of  hydrogen  and 
oxygen  takes  place.  Ramsay,®  Debierne,®  and  others  found  that 
there  is  some  excess  of  hydrogen  in  the  gases  evolved,  which  was 
attributed  by  Kernbaum  ^°  to  the  formation  of  some  HaO,  in 
the  solution.  It  should  be  pointed  out,  however,  that  the  rather 
large  excess  of  hydrogen  which  accompanies  radium  emanation 
in  the  usual  method  of  collecting  it  from  aqueous  solution  of 
radium  halides  is  to  be  attributed  to  another  cause.    The  halide 

•O.  IlSnigschmId,  Sitzb.  Akad.  Wise.  Wien,  Ila,  121,  1979   (1912). 
'P.  Curie  and  A.  Debierne,  Comp.  rend.  132,  770  (1901). 
"W.  Ramsay,  J.  Chcm.  Soc,  Lond..  91i.  931    (1907). 
»A.  Debierne,   Comp.  rend,  148,  703    (1909). 
"M.  Kernbaum,  Lc  Radium,  C,  225-8  (1909). 


QUALITATIVE  RADIOCHEMICAL  EFFECTS  49 

acid  which  is  also  present  in  the  solution  is  decomposed  into 
hydrogen  and  free  halide.  The  latter  combines  with  the  mer- 
cury in  the  collecting  system,  leaving  the  corresponding  hydro- 
gen in  excess  of  the  oxygen.  The  rate  of  the  decomposition  of 
water  by  radium  and  by  radium  emanation  has  been  quantita- 
tively investigated  by  a  number  of  authorities,  whose  work  will 
be  fully  reported  in  subsequent  chapters. 

It  may  not  be  amiss  to  mention  here  that  the  decomposition 
of  H2O  in  any  form  by  the  a  rays  renders  the  practice  of  sealing 
radium  salts  in  small  tubes  for  long  periods  of  time  a  dangerous 
one  unless  certain  precautions  are  observed.  Accidents  involving 
serious  loss  of  radium  have  occurred  through  the  explosion  of 
tubes  by  the  accumulated  pressure  of  hydrogen  and  oxygen.  It 
appears  to  be  dangerous  to  heat  an  old  tube  or  to  exert  any 
mechanical  stress  upon  it.  It  is  possible  that  weakening  of  the 
glass  container  by  the  continued  radiant  bombardment  en- 
hances the  danger  through  devitrification  of  the  glass.  A  far- 
reaching  disintegration  of  quartz  containers  by  radium  rays  has 
been  reported.^^  The  principal  precaution  to  be  observed  in 
sealing  radium  salts  in  glass  containers  is  the  thorough  dehydra- 
tion of  the  salt,  which  should  be  accomplished  by  heating  for 
not  less  than  twenty  minutes  to  a  temperature  not  under  250°  C. 
Preferably,  the  salt  should  be  raised  to  a  red  glow  in  a  quartz 
dish  for  a  shorter  time.  A  good  criterion  that  a  temperature  has 
been  reached  at  which  complete  dehydration  takes  place  rapidly 
will  be  furnished  by  the  character  of  light  emitted  by  the  radium 
salt  after  heating.  The  light  should  show  the  intensely  blue 
rather  than  the  ordinary  pale  yellow  luminescence  of  radium 
salts.  The  blue  luminescence  is  a  result  of  the  effect  of  tempera- 
ture and  is  not  directly  connected  with  the  degree  of  dehydra- 
tion, since  the  intense  blue  light  persists  even  under  water  as 
long  as  any  salt  remains  undissolved.  Karrer  and  Kabakjian  ^^ 
have  made  a  study  of  this  blue  luminescence  and  attribute  it  to 
the  formation  of  a  double  salt  of  radium  and  barium.  This  ap- 
pears difficult  to  reconcile  with  Honigschmid's  ^^  observation 
that  RaClg  of  the  highest  purity,  prepared  for  atomic  weight  de- 

"  Rutherford,  "Radioactive  Substances"  (1913),  p.  308.  Honigschmid, 
Sitzb.  Akad.  Wiss.  Wien,  Ila,  120,  1G24  (1911)  ;  St.  Meyer  and  V.  F.  Hess, 
ibid,  121,  255   (1912). 

"E.  Karrer  and  D.  H.  Kabakjian,  J.  Franklin  Inst.,  186.  317-40   (1918). 

"Q,  Honigsclimid,  Sitzb.  Akad.  Wfss,  Wien,  Ila,  IgO,  16^7-52   (191Q), 


60  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

termination,  showed  the  blue  color  in  a  very  enhanced  degree 
after  fusing.  The  blue  light  does  not  remain  constant  but  dies 
out  rapidly  in  the  course  of  a  few  days  to  a  small  fraction  of  the 
original  intensity,  but  still  remains  more  bluish  or  lavender  than 
the  light  from  salts  which  have  not  been  highly  heated. 

22.     Coloration  of  Glass  and  Minerals. 

The  color  produced  in  glass  and  many  transparent  minerals 
by  radium  rays  and  other  forms  of  radiation  has  been  a  fre- 
quent subject  of  investigation,  without  the  establishment  of  a 
final  theory  of  its  nature.  C.  Doelter^*  has  devoted  a  monograph 
to  the  experimental  and  descriptive  phases  of  the  subject.  Many 
attempts  have  been  made  to  find  a  connection  between  the  color 
produced  and  the  presence  of  some  constituent  of  the  glass  or 
mineral.  Most  glasses  are  colored  either  violet  or  brown,  and  it 
has  been  stated  that  soda  glasses  take  the  violet  and  that  potash 
glasses  take  the  brown  shades.  Others  would  attribute  the  violet 
to  manganese,  as  appears  to  be  true  for  the  coloration  by  ordi- 
nary light  of  glass  containing  manganese.  Bancroft  ^^  has  pro- 
posed a  physical  theory  depending  on  the  partial  coagulation  of 
coloring  material  in  the  colloidal  state  until  a  particle  of  a  cer- 
tain size  is  produced  capable  of  scattering  some  wave  lengths  and 
transmitting  others,  which  coagulating  process,  he  believes,  might 
be  stimulated  by  radiation.  Meyer  and  Przibram  ^®  found  that 
the  photo-electric  effect  is  increased  in  glass,  and  more  markedly 
in  fluorspar  and  kunzite,  that  had  been  colored  by  radiation  with 
radium  rays,  and  therefore  favored  a  physical  theory  of  the  eU 
feet. 

It  does  not  appear  possible  at  present  to  formulate  a  satis-* 
factory  theory  of  the  coloring  effects,  nor  to  decide  whether  they 
are  chemical  or  physical  in  nature.  Very  great  difficulties  are 
encountered  in  trying  to  ascribe  the  color  to  any  definite  com- 
ponent, though  it  seems  to  be  rather  generally  agreed  that  the 
presence  of  impurities,  possibly  in  extremely  minute  quantity 
beyond  the  range  of  chemical  determination,  influences  the  color 
production.    This  would  be  suggested  by  the  erratic  differences 

"C.  Doclter,  "Das  Radium  iind  die  Farben"    (1910). 
»W.  D.  Bancroft,  Jour.  Phys.  Chcm.  22,  601  (1918). 

'•St.  Meyer  and  K.  Przibram,  Sifzh,  Akad.  Wiaa.  Wicn,  Ila,  121,  14^4 
(J912), 


QUALITATIVE  RADIOCHEMICAL  EFFECTS  51 

found  for  the  same  mineral  from  different  localities.  Goldstein  ^^ 
estimates  that  impurities  amounting  to  not  more  than  one  part 
in  a  million  produce  color  effects  under  the  influence  of  cathode 
rays.  The  confusion  that  arises  in  attempting  to  settle  on  some 
certain  component  or  impurity  as  responsibile  for  the  color  may 
be  illustrated  by  some  of  the  following  observations.  Meyer  and 
Przibram  {loc.  cit.)  report  that  they  have  observed  the  produc- 
tion of  the  violet  and  of  the  brown  color  simultaneously  on  dif- 
ferent parts  of  the  same  glass  vessel,  which  were  subjected  to  a 
difference  only  in  the  intensity  of  the  radiation ;  while,  in  general, 
difference  in  intensity  or  even  the  kind  of  radiation  influences 
only  the  rate  at  which  color  is  produced.  An  outer  glass  tube 
enclosing  an  inner  one  (of  the  same  glass)  containing  radium 
salt,  takes  on  the  same  color  as  the  inner  one,  though  more  slowly, 
although  the  outer  one  receives  no  a  radiation  and  a  different 
intensity  of  penetrating  radiation  from  that  received  by  the  inner 
one.  Hard  glasses  high  in  silica,  of  the  pyrex  or  Jena  type,  in- 
variably take  the  brown  color,  but  silica  vessels,  including  the 
transparent  variety  made  from  pure  fused  quartz,  take  the  same 
violet  color  as  ordinary  soft  glass.  Lead  glass  is  colored  brown. 
In  all  cases  the  glass  appears  finally  to  become  saturated  and  the 
color  no  longer  deepens.  Thick  layers  of  glass  appear  to  be  more 
intensely  colored  on  account  of  the  depth  of  layer.  Very  thick 
glass,  like  the  walls  of  a  desiccator,  becomes  almost  opaque 
upon  prolonged  radiation.  The  power  of  luminescing  diminishes 
as  the  coloring  increases.  (Mme.  Curie,  "Radioactivite,"  II,  p. 
219  [1910].) 

The  color  produced  in  glass  and  minerals  by  radium  rays 
and  by  cathode  rays  can  be  discharged  by  heating  almost  to  the 
softening  point  of  glass.  The  same  color  is  again  restored  by 
renewed  radiation,  and  the  cycle  may  be  repeated,  apparently  in- 
definitely, without  any  fatigue  effect. 

As  a  result  of  an  extended  investigation  of  the  coloring  and 
thermoluminescence  produced  in  artificial  salts  and  natural  min- 
erals by  various  forms  of  radiation  JMeyer  and  Przibram  ^^  were 
led  to  discard  definitely  the  idea  of  the  influence  of  impurities, 
and  to  favor  a  return  to  the  theory  frequently  put  forward,  of 
colloidal  coloring  by  metallic  particles.  Attempts  to  distinguish 
discrete  particles  by  means  of  the  ultra-microscope  were  unsuc- 

"E.  Goldstein,  Ann.  d.  Physik,  54,  371   (1895)  ;  "Nature,"  94,  494   (1914). 
18  S.  Meyer  and  K.  Przibram,  Hitzh.  Akad.  Wise.  Wien,  123,  653  (1914). 


52  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

cessful  except  in  the  case  already  known  of  the  heating  of  rock 
salt  previously  radiated. 

It  has  been  shown  by  Rutherford  ^^  and  by  Joly  ^^  that  the 
depth  of  the  layer  of  glass  or  mineral  colored  by  a  rays  corre- 
sponds to  the  range  of  a  particles  in  the  given  substance.  Joly 
first  pointed  out  that  the  so-called  "pleochroic  halos,"  small  dark 
spots  in  certain  kinds  of  mica  (biotite,  cordierite,  and  musco- 
vite) ,  are  due  to  coloring  produced  by  minute  radioactive  centers 
in  the  mineral.  Joly  ^^  and  Joly  and  Fletcher  ^2  have  made  an 
extended  study  of  the  subject,  showing  that  the  diameters  of  the 
concentric  rings  constituting  the  halo  correspond  to  the  ranges  of 
the  different  sets  of  a  particles  in  the  uranium-radium  series,  and 
that  there  is  a  relation  between  the  development  of  the  halo  and 
the  geological  age  of  the  mineral. 

23.    Thermo-luminescence  Produced  by  Radiation. 

It  has  been  found  by  many  observers  that  salts,  glass,  min- 
erals, and  other  substances  after  being  exposed  to  radium  or  to 
cathode  rays  become  luminous  in  the  dark  at  temperatures  from 
40°  to  200°  C.  This  appears  to  be  due  to  an  effect  of  the  radia- 
tion which  is  as  yet  little  understood.  The  mistake  has  been 
rather  commonly  made  of  supposing  that  there  is  a  close  con- 
nection between  the  discharge  of  color  produced  in  glass,  for  in- 
stance (see  preceding  paragraph),  and  the  thermoluminiscent 
effect.  However,  it  has  recently  been  pointed  out  by  Lind  ^^  that 
thermoluminescence  can  usually  be  exhausted  at  about  200° 
without  at  all  diminishing  the  color,  which  is  not  discharged 
from  ordinary  violet  colored  glass  below  400°  to  500°  C,  so  that 
there  is  evidently  no  direct  connection  between  the  two  effects. 
Meyer  and  Przibram^*  have  made  an  interesting  observation 
which  has  been  confirmed  by  Lind  (lot.  cit.)  that  if  glass  col- 
ored brown  by  radium  radiation  be  heated  gently  until  its 
thermoluminescence  is  exhausted,  its  color  is  changed  to  the 
more  common  violet  tint  which  then  behaves  as  in  glass  originally 

"Rutherford,   "Radioactive   Substances"    (1913),   p.   307   et  acq. 

«>  J.  Joly,  Phil.  Mag.  (0)  13,  381  (1007). 

»J.  Joly,  ••Radioactivity  and  Geology"  (1909),  pp.  64-9;  Phil.  Mag.  (6) 
19,  327  (1910). 

"J.  Joly  and  A.  L.  Fletcher,  i6fd.,  19,  630  (1910). 

«S.  C.  Lind,  Journ.  Phya.  Chem.  24,  437   (1920). 

"St.  Meyer  and  K.  Przibrara,  Sitzb.  Akad.  Wiss.  Wien,  Ila,  121,  1414 
(1912). 


QUALITATIVE  RADIOCHEMICAL  EFFECTS  53 

colored  violet,  except  that  no  further  thermoluminescence  is  ex- 
hibited.   Upon  renewed  radiation  the  color  returns  to  brown. 

Freshly  radiated  glass  will  show  thermoluminescence  to  the 
well  rested  eye  at  temperatures  quite  below  the  boiling  point  of 
water,  while  glass  which  has  been  kept  for  three  or  four  years 
after  exposure  must  be  raised  to  the  neighborhood  of  200°  be- 
fore luminescence  sets  in  (Lind,  loc.  cit.). 

From  the  foregoing  statements  it  appears  that  if  the  colora- 
tion and  thermoluminescence  of  glass  and  minerals  are  due  to 
chemical  causes,  at  least  two  different  sets  of  reactions  are  in- 
volved which  may  have  little  or  no  connection  with  each  other. 
The  whole  subject  presents  an  attractive  field  for  further  investi- 
gation. 

Meyer  and  Przibram  (loc.  cit.)  examined  the  thermolumin- 
escence of  a  series  of  artificial  borates  and  silicates  of  the  alkalis, 
alkaline  earths  and  some  other  metals.  It  appeared  that  the 
wave  length  of  light  emitted  by  a  given  group  decreased  with  in- 
creasing atomic  weight  of  the  metal. 

24.    Luminescence  and  Phosphorescence  Produced  by  Radia- 
tion. 

Certain  substances  under  th^  influence  of  various  kinds  of 
radiation  emit  light  of  visible  wave  lengths  at  ordinary  and  even 
at  extremely  low  temperatures.  The  use  of  phosphorescent  zinc 
sulfide  screens  to  count  a  particles  by  means  of  the  scintillations 
produced  was  referred  to  in  §  12.  The  phenomenon  of  scintilla- 
tion is  not  only  important  as  a  means  of  counting  the  a  particles, 
but  historically  important  as  the  first  experimental  evidence  of 
the  individual  existence  of  atoms,  and  also  as  representative  of 
fluorescence  in  its  simplest  form.  Scintillations  can  be  individu- 
ally observed  and  counted  only  when  the  number  of  a  particles 
falling  on  a  given  area  of  screen  in  unit  time  is  limited.  When 
the  number  is  greatly  increased  the  screen  appears  to  be  uni- 
formly illuminated.  In  the  radium  luminous  paints,  radium  salts 
are  intimately  mixed  with  phosphorescent  zinc  sulfide,  which 
mixture  is  then  applied  to  a  dial  or  other  surface  to  be  illu- 
minated. These  luminous  mixtures  have  come  into  extensive 
use  oh  watch  and  clock  dials,  electric  push  buttons,  etc.,  and 
during  the  War  were  widely  used  for  illuminating  dials  on  aero- 


54  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

planes,  battleships,  or  in  any  place  where  it  was  desired  to  have 
a  feeble  light  not  visible  for  more  than  a  few  yards. 

The  nature  of  the  reaction  furnishing  the  light  is  not  thor- 
oughly understood.  Rutherford  ^^  has  proposed  a  theory  that  a 
phosphorescent  substance  contains  initially  a  large  number  of 
"active  centers"  or  molecular  aggregates  which  are  disrupted  by 
a  particles  with  the  emission  of  light.  Marsden  ^^  examined  the 
effect  of  intense  a  radiation  on  phosphorescent  zinc  sulfide  and 
found  that  the  intensity  of  the  light  emitted  falls  off  rapidly. 
The  number  of  scintillations  remains  constant,  but  the  light 
emitted  from  each  scintillation  becomes  feebler,  owing  to  the 
gradual  exhaustion  of  the  active  centers.  Rutherford  has  calcu- 
lated that  a  single  a  particle  destroys  all  the  centers  in  its  path 
within  a  radius  of  about  1.3x10"^  cm.  for  ZnS,  and  about  2.5x10"^ 
cm.  for  willemite.  The  decay  curves  of  luminous  radium  paints 
such  as  used  by  the  British  Admiralty  have  been  carefully  deter- 
mined by  Paterson,  Walsh,  and  Higgins,^^  whose  results  are  not 
only  of  great  practical  but  of  much  theoretical  interest.  After 
mixing  with  a  radium  salt  the  luminosity  of  the  paint  increases 
owing  to  the  growth  of  radium  emanation  and  active  deposit; 
after  ten  to  twenty  days  this  increase  is  counterbalanced  by 
the  decay  of  the  ZnS,  so  that  a  maximum  is  attained.  The  lumi- 
nosity then  begins  to  fall,  slowly  at  first  and  then  more  rapidly. 
At  the  end  of  six  or  seven  weeks  the  rate  of  decrease  becomes  ex- 
ponential with  the  time  according  to  the  equation:  B/Bo=e-^S 
in  which  Bo  and  B  are  the  luminosities  initially  and  at  any  time 
t,  and  k  is  the  decay  constant.  Between  40  and  200  days  the 
rate  of  decay  follows  this  law  closely,  and  then  becomes  slower. 
After  500  days  a  practically  constant  value  is  attained  of  about 
1/4  the  luminosity  at  maximum.  Walsh  ^^  has  proposed  a  "re- 
covery" theory,  according  to  which  a  state  of  equilibrium  i& 
reached  between  the  two  opposing  reactions: 

Decay  of  active  centers  ^  Regeneration  of  active  centers. 

Walsh  established  kinetic  equations  and  showed  that  they  fit 
such  an  assumption  without  any  hypothesis  as  to  the  nature  of 
the  two  reactions. 

»E.  E.  Rutherford,  Proc.  Roy.  8oc.  83A  5C1   (1910). 
ME.  Marsden,  ibid.  83A,  548   (1910). 

"  C.  C.  Patterson,  J.  W.  T.  Walsh,  and  W.  F.  Higgins,  Proc.  Phya.  Soc, 
Lond.  29,  215-49   (1917). 

«J.  W.  T.  Walsh,  Proo.  Roy.  8oc.  93A  550  (1917). 


QUALITATIVE  RADIOCHEMICAL  EFFECTS  55 

Both  the  luminosity  and  rate  of  decay  of  the  luminous  com- 
pounds depend  upon  the  quality  of  the  phosphorescent  ZnS  and 
the  proportion  of  radium  in  the  mixture.  Evidently  it  is  undesir- 
able to  use  for  any  purpose  a  more  luminous  paint  than  is  re- 
quired, both  on  account  of  the  initial  cost  of  the  radium  and  the 
shortened  life  of  the  compound  through  more  intense  radiation. 
The  upper  limit  of  radium  is  about  one  part  to  four  thousand  of 
ZnS.  Below  this,  various  grades  are  used  down  to  one  part  in 
one  or  two  hundred  thousand.  The  purity  of  the  radium  salt 
employed  should  be  between  10  and  100%.  A  very  interesting 
fact  pointed  out  by  Patterson,  Walsh  and  Higgins  {loc.  cit.) 
is  that  the  rate  of  decay  and  luminosity  of  a  paint  are  three 
to  four  times  smaller  after  application  to  a  dial  than  before. 
This  is  evidently  due  to  the  partial  absorption  of  the  a  radia- 
tion by  the  binding  agent  used  to  make  the  paint  adhere  to  the 
dial.  It  is  very  fortunate  that  the  great  loss  in  luminosity  is 
compensated  by  a  corresponding  lengthening  of  its  life. 

On  account  of  the  long  life  of  radium  and  the  consequent 
waste  in  applying  it  to  a  dial,  the  use  of  which  is  limited  to  a  few 
years,  it  has  been  proposed  ^^  that  the  corresponding  member  of 
the  thorium  series,  meso-thorium,  should  be  used,  which  has  a 
half-period  of  6.7  years  ^°  and  would  be  effective  for  a  period 
sufficient  for  all  practical  purposes.  Walsh  ^^  has  discussed  the 
theory  of  meso-thorium  paints  and  developed  the  theoretical  de- 
cay curves.  Meso-thorium  itself  emits  no  a  radiation,  which 
must  be  generated  by  the  growth  of  radio-thorium  with  a  half 
period  rate  of  1.876  years,^^  which  involves  the  disadvantage  of 
requiring  the  "ripening"  of  meso-thorium  salts  for  one  or  more 
years  before  using,  but  the  advantage  that,  if  used  before  a  radia- 
tion attains  a  maximum,  its  growth  will  in  part  compensate  the 
deterioration  of  the  ZnS.  It  has  been  reported  that  the  use  of 
radio-thorium  for  luminous  paints  has  become  common  in  the 
Swiss  watch  industry.  The  parent  meso-thorium  is  employed 
therapeutically  through  the  use  of  its  y  radiation,  and  at  suitable 
intervals,  a  year  or  two,  the  salt  is  put  into  solution  and  radio- 
thorium  precipitated  for  luminous  preparations,  the  meso-tho- 
rium being  then  returned  into  therapeutic  use.    It  is  questionable, 

"  R.  B.  Moore,  Bull.  Am.  Inst.  Min.  Met.  Engs.,  Aug.,  1918. 
""L.  Meitner,  Phys.  Zeit.  19,  257-63    (1918). 
«ij.  W.  T.  Walsh,  Proc.  Roy.  Soc.  93  A,  562-5   (1917). 
»B.  Walter,  Phya.  Zeit.  18,  584   (1917). 


56  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND   ELECTRONS 

however,  if  the  use  of  such  a  short-lived  product  as  radio-thorium 
in  the  luminous  paint  industry  can  be  recommended. 

The  method  of  preparing  phosphorescent  zinc  sulfide  has  not 
been  fully  described  in  the  literature.  Crystalline  ZnS  (Sidot's 
blende) ,  also  called  hexagonal  ZnS,  can  be  prepared  in  a  variety 
of  ways.  Its  phosphorescent  qualities  vary  greatly  and  appear 
to  depend  on  at  least  two  factors,  the  heat  treatment  and  the 
presence  of  small  quantities  of  certain  impurities.  The  methods 
in  commercial  use  have  been  carefully  guarded  and  it  is  not  pos- 
sible to  give  full  details.  The  heat  treatment  consists  in  raising 
the  ZnS  mixture  for  a  limited  time  out  of  contact  with  air  to 
a  temperature  at  which  incipient  crystallization  begins.  The  de- 
velopment of  large,  coarse  crystals  is  to  be  avoided ;  on  the  other 
hand,  the  crystalline  structure  should  be  distinct  after  cooling. 
Fine  grinding  of  the  crystals  damages  their  luminescent  qualities. 
The  temperature  and  time  of  heating  will  depend  to  a  large  ex- 
tent upon  other  experimental  conditions.  800°  to  900°  C.  at 
least  is  necessary  for  best  results  though  some  phosphorescence 
begins  to  be  developed  as  low  as  600°.  1300°  appears  to  be  the 
upper  limit  at  which  favorable  results  can  be  obtained.  With 
respect  to  the  impurities  necessary  there  is  the  widest  divergence 
of  views.  It  has  even  been  claimed  that  the  purest  possible  ZnS 
is  best.  This  has  been  definitely  disproved  by  experiments  of 
C.  W.  Davis  ^^  in  the  laboratory  of  the  U.  S.  Bureau  of  Mines. 
Starting  with  a  very  pure  zinc  spelter  and  taking  great  precau- 
tions with  all  the  reagents  used,  it  was  possible  to  prepare  ZnS 
of  such  purity  that  no  heat  treatment  would  develop  any  phos- 
phorescent properties  towards  ordinary  light  and  only  a  faint 
luminescence  under  the  action  of  relatively  large  quantities  of 
radium  emanation.  The  admixtures  which  have  been  mentioned 
as  advantageous  are  manganese,  copper,  or  bismuth  salts,  sodium 
chloride,  and  salts  of  the  rare  earths.  Chemical  examination  of 
some  commercial  samples  of  phosphorescent  ZnS  has  failed  to 
disclose  the  effective  impurities  and  it  is  quite  possible  that  the 
quantities  required  are  not  chemically  determinable.  It  also 
appears  that  neutral  salts  are  sometimes  added  to  "camouflage" 
the  presence  of  the  effective  agents. 

The  properties  of  phosphorescence  toward  ordinary  light  and 
of  response  to  a  radiation  are  not  necessarily  coincident,  and  for 

»8  Unpublished  results  of  C.  W.  Davis. 


QUALITATIVE  RADIOCHEMICAL  EFFECTS  57 

certain  purposes  it  is  desirable  to  obtain  a  rather  non-phosphor- 
escent preparation  for  radium  paint. 

The  nature  and  proportions  of  the  microchemical  admixtures 
are  varied  according  to  the  use  for  which  a  given  luminous  ma- 
terial is  intended.  Increased  intensity  seems  always  to  be  at- 
tained at  the  expense  of  the  duration. 

Many  other  phosphorescent  substances  respond  to  various 
kinds  of  radiation.  ZnS  is  the  most  sensitive  to  a  rays;  barium 
platinocyanide  is  more  sensitive  toward  |3,  y,  and  X  rays.  Wil- 
lemite,  natural  and  artificial,  responds  to  both  a  and  penetrating 
radiation.  Many  minerals  have  been  found  responsive  to  cathode 
rays,  though  different  specimens  of  the  same  mineral  show  great 
variations.  Kunz  and  Baskerville  ^*  have  described  the  luminous 
effects  produced  in  different  gems  by  radium  rays. 

There  are  among  the  alkaline  earth  sulfides  also  a  number 
of  compounds  or  mixtures  which  are  strongly  phosphorescent  fol- 
lowing exposure  to  light,  which  do  not  respond  to  radiation  by 
radium  rays.  They  have  been  fully  treated  by  Klatt  and  Len- 
ard,^^  by  Wiedemann  and  Schmidt,^^  by  Waentig,^^  and  others. 
It  is  beyond  the  scope  of  the  present  work  to  go  into  the  subject 
further  than  to  point  out  that  it  appears  quite  well  established 
that  the  reactions  are  physico-chemical  in  nature,  that  the  pres- 
ence of  two  or  preferably  three  components  is  necessary  to  pro- 
duce a  responsive  compound  and  that  in  all  probability  the  for- 
mation of  a  double  compound  in  crystalline  form  is  necessary. 
According  to  modern  ideas  crystals  are  molecular  aggregates  so 
that  there  is  no  conflict  with  this  view  and  Rutherford's  theory 
of  active  centers.  Waentig  treats  the  subject  from  the  physical- 
chemical  view  of  solid  solution. 

25.    General  Character  of  the  Chemical  Effects  of  the  Rays  of 
Radium. 

Before  proceeding  in  the  following  chapters  to  consider  in  de- 
tail the  quantitative  side  of  the  chemical  reactions  brought  about 
by  the  radiations  from  radium  and  other  sources,  it  will  be  of 

8*G.  Kunz  and  C.  Baskerville,  Science  18,  769    (1903). 
sop.  Lenard  and  V.  Klatt,  Wied.  Ann.  38,  90   (1889), 

38  E.  Wiedemann  and  G.  C.  Schmidt,  ibid.  54,  604  (1895)  ;  56,  201  (1895)  ; 
64,  78   (1898). 

«P.  Waentig,  Zeit.  phys.  Chem.  51,  435-72  (1905). 


58  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

some  interest  to  touch  briefly  on  some  of  their  general  character- 
istics and  to  compare  them  with  photochemical  reactions.  The 
wide  variety  of  chemical  actions  brought  about,  particularly  by 
the  a  rays,  is  surprising,  and  one  must  be  struck  by  the  univer- 
sality of  the  phenomenon  of  chemical  change  by  corpuscular  ra- 
diation. This  is  in  marked  contrast  with  photochemical  action, 
where  the  specific  nature  of  the  reaction  and  of  the  system  being 
acted  on  depends  entirely  upon  the  wave-length  of  the  light,  and 
its  capability  of  being  absorbed  by  the  given  system.  The  highly 
specific  and  selective  nature  of  photochemical  reactions  is  their 
chief  characteristic;  whereas,  we  find  that  a  and  p  rays,  in  their 
passage  through  molecules,  are  almost  universally  capable  of 
changing  them  chemically;  their  action  does  not  depend  upon 
any  reciprocal  relation  with  the  atom  or  molecule  affected,  sim- 
ilar to  a  resonance  effect.  Owing  to  the  tremendous  kinetic 
energy  of  the  a  particles  they  always  ionize  and  frequently  pro- 
duce chemi(!al  changes  in  the  substances  through  which  they 
pass.  Several  different  views  have  been  expressed  regarding  the 
mechanism  of  the  reactions,  which  may  be  classified  in  general 
terms  as:  catalytic,  mechanical  and  electrical.  Discussion  of 
the  theories  will  be  deferred  until  after  the  experimental  data 
have  been  presented,  but  it  may  not  be  amiss  to  state  by  way  of 
anticipation  that  the  evidence  supporting  an  electrical  or  ioniza- 
tion theory  of  the  chemical  effects  appears  to  have  much  in 
its  favor  and  will  be  given  full  consideration  in  Chapters  7  to  9. 


Chapter  5. 

Chemically  Quantitative  Investigations  in  Liquid 

Systems. 

26.    Decomposition  of  Water  by  Radium  Salts  in  Solution. 

The  first  observations  of  the  decomposition  of  water  by  ra- 
dium in  solution  were  qualitative,  as  has  already  been  men- 
tioned. As  soon  as  a  standard  for  the  measurement  of  radium 
was  made  possible  through  the  researches  of  Mme.  Curie,  it  ap- 
peared, to  be  very  simple  to  measure  the  amounts  of  hydrogen 
and  oxygen  liberated  from  solution  per  unit  of  radium  in  unit  of 
time.  The  wide  variations  in  the  values  reported,  by  different 
authorities  were  sufficient,  however,  to  convince  one  that  the  sub- 
ject was  more  complicated  than  was  at  first  anticipated. 

Although  the  decomposition  is  produced  mainly  by  the  a  rays, 
which  would  be  entirely  absorbed  by  very  thin  layers  of  water, 
and  which,  so  far  as  those  from  radium  alone  are  concerned, 
would  expend  all  their  energy  within  the  liquid  system,  additional 
factors  must  be  considered.  In  the  first  place,  it  was  not  at  once 
recognized  that  the  decomposition  is  really  due  to  a  radiation. 
It  should  be  mentioned  here  and  reiterated  as  later  occasions 
arise,  that  the  first  attempts  to  explain  the  chemical  effects  of 
radium,  somewhat  naturally  but  unfortunately,  took  the  uncer- 
tain paths  of  catalysis,  which  was  perhaps  regarded  as  peculiarly 
suited  to  explain  the  effects  of  the  radioactive  changes,  them- 
selves so  puzzling  to  chemists  in  the  beginning.  It  was  not  until 
1910  that  Usher  ^  stated  that  the  reactions  are  due  to  a  rays  and 
can  in  no  sense  be  regarded  as  catalytic.  This  means  simply 
that  more  definite  laws  have  been  established — which  may  later 
be  accomplished  for  other  classes  of  reactions  now  classed  as 
catalytic.    (See  also  §  58.) 

The  second  factor  which  produced  confusion  and  which  goes 
hand  in  hand  with  the  failure  to  recognize  that  the  decompo- 
sition is  due  to  a  rays,  w^as  the  false  idea  that  the  seat  of  reaction 

'  F,  L,  Usher,  Journ.  Chcm.  Hoc.  Lond.  97j ,  389-405  (1910), 


60  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

is  confined  to  the  radium  in  solution;  whereas,  in  reality,  radium 
emanation  distributes  itself,  as  would  any  slightly  soluble  gas, 
between  the  liquid  and  gas  phases  in  a  proportion  dependent 
upon  the  temperature.  The  a  radiation  from  the  gas  phase  is 
much  less  effective  than  that  in  the  water,  since  part  of  the  ra- 
diation is  absorbed  by  the  walls  of  the  container.  In  some  early 
experiments  a  small  amount  of  water  was  used  to  hold  the  ra- 
dium salt  in  solution  in  a  relatively  large  vessel,  thus  greatly 
reducing  the  efficiency  of  absorption  of  the  radiation  by  the 
water  to  be  acted  on.  Taking  into  account  the  partition  of  the 
emanation  and  its  active  products,  it  is  evident  that  not  only  the 
relative  volumes  of  gas  and  liquid  phases,  but  also  the  tempera- 
ture, the  surface  of  the  liquid  phase,  and  the  absolute  dimensions 
and  the  shape  of  the  containing  vessel  would  influence  the  amount 
of  water  decomposed  by  a  given  quantity  of  radium  in  solution. 
Neglect  of  these  factors  accounts  for  the  wide  variations  in  dif- 
ferent observations.  Maximum  decomposition  can  be  attained 
only  in  the  absence  of  any  gas  phase,  which  is  difficult  to  realize 
on  account  of  the  evolution  of  hydrogen  and  oxygen.  These 
conditions  have  perhaps  never  been  fulfilled  experimentally  for 
a  radium  solution,  but  an  indirect  calculation  will  give  the  maxi- 
mum sought.  Duane  and  Scheuer  ^  found  for  radium  emanation 
in  equilibrium  with  Ra  A,  B,  and  C:  2.9  cm.^  (per  hour  per  1 
curie)  of  electrolytic  gas.  Assuming  that  the  decomposition  pro- 
duced by  the  a  particles  of  radium  is  proportional  to  the  ioniza- 
tion or  to  the  energy  absorbed  (see  Table  I,  page  28),  one  cal- 
culates for  the  maximum  decomposition  of  water  by  a  radium 
solution  in  equilibrium  with  Ra  A,  B,  and  C:  3.6  cm.^  of  hydro- 
gen and  equivalent  oxygen  per  hour  per  gram  of  radium.  Fuller 
consideration  of  the  results  of  Duane  and  Scheuer  and  of  Usher 
on  the  decomposition  of  water  by  radium  emanation  will  be  re- 
served for  the  following  chapter. 

27.    Formation  of  Hydrogen  Peroxide  in  Water. 

It  has  been  observed  by  Runge  and  Bodliinder,^  Ramsay,* 
Kernbaum,^  and  Duane  and  Scheuer  ^  that  the  mixture  of  hydro- 

»W.  Duane  and  O.  Schouer.  Lc  Radium  10,  42   (1913). 

«C.  Runge  and  G.  BodlUnder,  Ber.  35,  3G05  (1902). 

*W.  Ramsay,  Jour.  Chcm.  Soc.  Lorul.  Olj,  931   (1907). 

"M.  Kornbauni.  Comp.  rend.  14S,  70.'»  ;  Lc  Radium  i\,  22r>  (1909). 

«W.  Duane  pnd  O.  Scheuer,  Le  Radium  10,  33-40  (1910), 


CHEMICALLY  QUANTITATIVE  INVESTIGATIONS  61 

gen  and  oxygen  obtained  by  the  decomposition  of  water  by  ra- 
dium radiation  contains  an  excess  of  hydrogen.  The  excess  is 
greater  in  the  early  stages  of  the  reaction  and  has  been  found 
to  amount  to  an  excess  of  36%  above  theoretical  in  one  case.® 
Kembaum  ^  showed  that  hydrogen  peroxide  is  formed  in  the  wa- 
ter in  an  amount  equivalent  to  the  deficiency  of  oxygen  in  the 
gaseous  mixture.  As  the  quantity  of  hydrogen  peroxide  accumu- 
lates in  the  solution  a  point  is  reached  where  its  rate  of  decom- 
position just  balances  the  new  formation,  under  which  condition 
of  dynamic  equilibrium  the  gases  evolved  would  have  normal 
composition.  This  explains  the  gradual  diminution  in  the  ob- 
served excess  of  hydrogen.  It  is  also  conceivable  that  under  a 
slightly  changed  condition,  such  as  rise  of  temperature,  decom- 
position of  peroxide  might  for  a  time  exceed  its  formation  which 
would  result  in  an  excess  of  oxygen.  The  decomposition  of  H^Og 
is  partly  spontaneous  and  partly  produced  by  the  radiations  (see 
following  section).  Kernbaum  {loc.  cit.)  reports  that  the  action 
of  the  penetrating  rays  results  exclusively  in  the  formation  of 
H2O2,  the  gas  evolved  being  pure  hydrogen.  Kernbaum  found 
that  the  energy  utilized  in  the  formation  of  HgOg  is  about  1/10000 
of  the  total,  and  Mme.  Curie  ^  estimates  that  the  available  energy 
from  the  penetrating  radiation  is  about  1/100  of  the  total,  and 
that  therefore  the  energy  utilization  of  penetrating  radiation  is 
about  1%.  Kailan  ^  on  a  similar  basis  estimates  from  his  results 
about  1.25%. 


28.    Reactions  Produced  by  Penetrating  Rays. 

A  method  of  very  general  use  in  the  examination  of  the  chemi- 
cal effects  of  the  rays  of  radium,  particularly  in  liquid  systems, 
consists  in  exposing  the  system  to  the  penetrating  rays  from  a 
closed  preparation  of  radium,  usually  sealed  in  glass.  This 
method  has  the  advantage  of  great  simplicity  of  manipulation, 
and  of  constancy  of  the  source  of  radiation  for  any  desired 
length  of  time.  The  disadvantages  consist  in  having  to  use  rela- 
tively large  quantities  of  radium  since  only  the  penetrating  rays 
are  available,  and  in  having  to  be  content  with  only  a  rough  esti- 

'M.  Kernbaum,  Lc  Radium  7,  242    (1910). 

"Mme.  Curie,  "Trait6  de  Radioactivity"    (1910),  Vol.  II,  p.  251. 

•A.  Kailan,  SitzJi.  Akad.  Wisa.  Wien  Ha,  120,  1227  (1911). 


62  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

mation  of  the  proportion  of  the  radiation  that  is  effectively- 
absorbed. 

Experiments  of  Kalian.  A  very  extensive  series  of  experi- 
ments has  been  carried  out  with  large  quantities  of  radium  in 
the  Institut  f.  Radiumforschung  in  Vienna  by  Anton  Kailan,  who 
has  investigated  a  large  number  of  inorganic  and  organic  reaction 
of  very  varied  character. 

The  decomposition  of  HgOg  ^^  was  investigated  at  13-15°  and 
at  25°  in  paraffined  and  in  bare  glass  vessels,  and  was  found  to 
take  place  approximately  according  to  a  first  order  equation. 
The  temperature  coefficient  is  low,  1.2  per  10°  C,  which  is  a 
property  common  to  most  radio-  and  photo-chemical  reactions. 
The  velocity  of  decomposition  was  found  to  increase  with  the 
strength  of  the  radium  preparations,  though  not  quite  propor- 
tionately to  it. 

Using  a  preparation  containing  239  mgs.  of  radium  element, 
Kailan  ^2*  was  able  to  confirm  Kernbaum's  discovery  (see  pre- 
ceding section)  of  the  production  of  HgOg  in  water. 

Kailan  also  studied  the  decomposition  of  the  alkaline  (Na 
and  K)  iodides,^^  and  later  of  the  alkaline  earth  iodides,^^  in 
aqueous  solution,  as  well  as  the  effect  of  the  penetrating  radia- 
tion on  several  other  inorganic  compounds.^-*  The  decomposition 
was  greater  for  KI  than  for  Nal,  and  greater  for  both  salts  in 
acid  than  in  neutral  solution.  The  rate  of  decomposition  rises 
very  rapidly  with  the  addition  of  the  first  quantities  of  acid 
(5x10-^  molar  doubles  the  rate),  but  afterwards  the  increase  is 
slow  for  further  increase  of  acid.  The  decomposition  of  the 
iodides  also  increases  with  the  salt  concentration,  but  far  below 
direct  proportionality. 

A  somewhat  puzzling  result  obtained  by  Kailan  in  connection 
with  the  decomposition  of  KI  is  that  the  rate  in  neutral  solu- 
tion has  a  negative  temperature  coefficient.  An  explanation  may 
be  sought  in  the  well-known  fact  that  radiochemical  reactions 
usually  have  either  no  temperature  coefficient  or  very  small  ones, 
which  would  account  for  no  additional  decomposition  with  in- 
crease of  temperature.  The  actual  observed  diminution  in  rate 
would  then  be  explained  by  the  ordinary  influence  of  tempera- 

«>A.  Kailan,  Sitzh.  Akad.  Wiss.  Wien  Ila,  120,  1213-28   (1911). 
"A.  Kailan,  ihid.,  120,  1373-1400   (1911). 
"A.  Kailan,  Ibid.,  122,  787-810  (1913). 
i-^Jbid.,  121,  1353-84  (1912). 


CHEMICALLY  QUANTITATIVE  INVESTIGATIONS  63 

ture  on  the  reverse  reaction  between  the  liberated  iodine  and 
alkali.  When  one  attempts,  however,  to  apply  the  same  rea- 
soning to  decomposition  of  KI  in  acid  solution,  which,  according 
to  Creighton  and  McKenzie,^^  also  has  a  negative  temperature 
coefficient,  the  explanation  becomes  more  difficult.  Kailan  fa- 
vors the  view  that  decomposition  of  KI  is  due  to  the  direct  de- 
composition of  electrolytically  undissoeiated  salt  molecules.  It 
appears  much  more  likely  that  the  radiation  first  acts  on  water 
to  produce  an  activated  (nascent)  form  of  oxygen  which  reacts 
with  KI  in  a  secondary  reaction. 

Penetrating  rays  were  found  by  Kailan  to  reduce  ferric  sulfate 
in  aqueous  solution,  similar  to  the  action  found  by  Ross^*  for 
ultraviolet  light.  The  decomposition  of  KBr  solution  was  found 
to  be  20-100  times  less  than  that  of  KI  under  the  same  condi- 
tions. Decomposition  of  CaClg  could  not  be  detected.  The  de- 
composition of  the  iodides  of  the  alkaline  earths  and  of  mag- 
nesium disclosed  the  same  general  relations  as  did  the  alkaline 
iodides.  No  relation  between  rate  of  decomposition  and  molec- 
ular weight  could  be  established. 

Comparing  the  effects  of  the  penetrating  rays  with  those  of 
ultraviolet  light,  Kailan  found  that  a  quartz  mercury  lamp  at 
8  cms.  distance  gave  the  same  amount  of  reaction  in  periods  of 
time  200-800  times  shorter  than  did  preparations  of  radium  con- 
taining 80-200  mgs.  of  element  placed  directly  in  the  liquid. 

Kailan  ^^  also  investigated  the  effect  of  penetrating  rays  on  a 
number  of  organic  compounds  and  reactions.  The  inversion  of 
cane  sugar  was  observed  and  referred  to  the  secondary  action  of 
a  primary  acid  formation,  which  was  confirmed  by  the  much 
smaller  effect  produced  in  grape  sugar.  Ester  formation  from 
alcohol  and  acid  is  not  notably  affected  by  penetrating  radia- 
tion. The  decomposition  of  esters  takes  place  to  some  extent, 
but  appears  to  be  more  of  the  nature  of  a  shattering  of  the 
molecules  than  of  an  ordinary  saponification.  The  conversion 
of  nitrobenzaldehyde  into  acid  was  produced  at  a  rate  of  10-20 
thousand  times  as  slowly  as  by  a  mercury  arc  lamp  at  8  cms. 
Chinon  and  oxalic,  malonic  and  tartaric  acids  showed  no  posi- 

"  H.  J.  M.  Creighton  and  A.  S.  McKenzie,  Amer.  Chem.  Journ.,  39,  474-93 
(1908). 

"W.  H.  Ross,  J.  Am.  Chem.  8oc.  28,  786   (1907). 

"A.  Kailan,  Sitzh.  AJcad.  Wiaa.  Wien  Ila,  121,  1385;  2127  (1912)  ;  122,  881 
(1913)  ;  12S,  583;  1427  (1914). 


64  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

tive  effects.  The  electrical  conductivity  of  fumaric  acid  is  raised 
and  that  of  maleic  acid  lowered  by  penetrating  rays,  with  the 
difference  that  the  magnitude  of  the  effect  is  about  equal  for  the 
two  acids  with  radium  rays,  but  much  greater  for  maleic  acid  in 
ultraviolet  light.  This  seems  to  justify  the  conclusion  that  the 
photo-equilibrium  between  the  two  stereo-isomers  would  differ 
from  that  reached  under  the  influence  of  p  and  y  rays. 

Kailan  ^^  *has  also  examined  the  effect  of  penetrating  radia- 
tion on  chloroform  and  carbon  tetrachloride  and  compared  the 
effect  on  the  former  with  that  produced  by  ultraviolet  light. 
The  radiation  from  80  mgs.  of  element  was  allowed  to  act  in  the 
absence  of  light  for  about  three  years.  In  both  cases  the  chief 
reaction  is  through  the  interaction  with  oxygen  of  the  air;  in  the 
case  of  chloroform  resulting  in  the  formation  of  hexachlorethane, 
in  the  case  of  carbon  tetrachloride  in  the  formation  of  chlorine, 
and  likewise  of  hydrogen  chloride  from  the  reaction  of  phosgene, 
primarily  formed,  with  the  water  present  in  the  compounds.  The 
total  decomposition  of  30-45  cm.^  of  CCl^  in  three  years  amounted 
to  %  to  %%,  while  about  twice  this  quantity  of  CHCI3  was 
changed  to  the  extent  of  %  ^  %%  in  the  same  time,  showing 
that  the  absolute  quantity  of  change  was  of  the  same  order  in 
both  cases.  Similar  effects  were  produced  by  ultraviolet  light 
in  about  1 /300th  of  the  time  required  for  penetrating  rays. 

The  effect  of  penetrating  radiation  on  toluene,  both  in  the 
presence  and  absence  of  water,  has  been  determined  by  Kailan,^^ 
using  80  mgs.  of  Ra  element  for  a  period  of  two  years.  The 
products  of  reaction  in  the  presence  of  air  were  benzaldehyde, 
benzoic  acid,  and  probably  formic  acid.  In  the  case  of  dry 
toluene,  less  than  l^%  was  changed  in  two  years.  Effects  of 
the  same  kind  and  magnitude  could  be  obtained  by  22  hours' 
radiation  with  a  quartz  mercury  lamp  at  8  cms.  The  effect  of  the 
penetrating  rays  from  110  mgs.  of  element  in  two  years  on  50 
cm.^  each  of  toluene  and  water  produced  about  three  times  as 
much  acid  as  in  the  case  of  dry  toluene.  About  70%  of  the 
acid  was  benzoic,  and  about  30%  formic.  Radiation  for  22  hours 
with  ultraviolet  light  produced  a  little  less  acid  than  the  two 
years  of  penetrating  radiation.  The  products  consisted  of  44% 
benzoic,  36%  formic,  and  20%  oxalic  acid. 

"A.  Kalian,  Sitzh.  Akad.  Wiss.  Wien  Ila,  126,  741   (1917). 
"A.  Kalian,  ibid.,  Ila,  128,  831-52   (1919). 


Chapter  6. 

Reactions  Produced  by  Radium  Emanation. 
(First  Experiments.) 

29.    Radium  Emanation  as  a  Source  of  Radiation. 

In  most  respects  radium  emanation  has  advantages  over  any 
of  the  other  forms  of  radioactive  matter  as  a  source  of  radiation 
in  the  study  of  the  production  of  chemical  reaction.  These  ad- 
vantages have  already  been  considered  in  some  detail  in  §  14. 

The  heat  evolution  from  one  gram  of  radium  in  equilibrium 
with  Ra  C  has  been  determined  by  Meyer  and  Hess  ^  to  be  132 
small  gram  calories  per  hour.  The  evolved  heat  is  generated  by 
the  absorption  of  the  various  radiations  in  the  matter  through 
which  they  pass.  Rutherford  -  has  calculated  the  following  dis- 
tribution: a  particles  (including  recoil  atoms),  from  Ra,  25.1 
cal.;  from  Emanation,  28.6;  from  Ra  A,  30.5;  from  Ra  C,  39.4; 
total  123.6;  p  rays  from  Ra  C,  4-^;  y  rays  from  Ra  C,  6.5;  grand 
total  for  radium  in  equilibrium  134.4-  This  agrees  well  with  the 
result  of  Meyer  and  Hess  obtained  under  conditions  where  only 
15%  of  the  Y  radiation  was  absorbed. 

For  radium  emanation  in  equilibrium  with  active  deposit,  the 
total  from  a  rays  and  recoil  atoms  would  be  109.3,  or,  including 
|3  rays,  would  be  113.6  cal.  These  heat  emissions  can  be  used  in 
calculating  the  energy  efficiency  for  any  given  chemical  reac- 
tion in  which  the  absorption  is  complete  within  the  system.  In 
cases  of  incomplete  absorption  in  the  chemical  system  more 
roundabout  methods  of  calculating  the  efficiency  must  be  re- 
sorted to. 

The  total  ionization  per  second  produced  by  radium  emana- 
tion when  mixed  with  air  in  cylinders  of  different  sizes  may 
be  approximately  estimated  by  means  of  the  empirical  formula 
of  Duane  and  Laborde,^  which  may  be  written  in  the  form: 

iSt.  Meyer  and  V.  F.  Bfess,  SitzJ).  Akad.  Wiss.  Wicn  Ila,  121.  603   (1912). 

*  Rutherford,  "Radioactive  Substances,"  p.  581    (1913). 

*  VVm.  Duane  and  A.  Labordo,  Lc  Radium  7,  1G2-4  (1910)  ;  Duanc,  Comp. 
rend.  140,  581;  786  (1905). 

65 


66  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

X  =  I  (max.)/13.5(l-0.572.S/V),  in  which  X  is  the  quantity  of 
emanation  produced  per  second  by  1  gram  of  radium,  I  (max.) 
is  the  saturation  current  in  electrostatic  units  after  3  hours 
when  emanation  is  in  equilibrium  with  its  decay  products,  S  is 
the  inner  surface  of  the  chamber  in  cm.^,  and  V  the  volume  in 
cm.^.  The  conversion  factor  from  gram-seconds  to  curies  of 
radium  emanation  is:  1  curie  =  4.795xl0^gm.secs.  The  formula 
of  Duane  and  Laborde  is  purely  empirical  and  does  not  apply 
accurately,  as  has  been  shown  by  Leaming,  Schlundt  and  Under- 
wood *  to  chambers  of  volumes  or  shapes  very  different  from 
those  employed  by  Duane  and  Laborde.  The  ionization  pro- 
duced in  gases  other  than  air  can  also  be  approximately  esti- 
mated by  applying  a  correction  for  the  specific  ionization  of  the 
given  gas  (Table  II). 

30.    Experiments  of  Cameron  and  Ramsay. 

In  1907  and  1908  Cameron  and  Ramsay  ^  carried  out  an  ex- 
tended series  of  experiments  on  the  chemical  action  of  radium 
emanation  on  water  and  on  a  number  of  gases  at  ordinary  tem- 
perature. Reactions  were  chosen  that  would  proceed  with  a 
change  in  pressure  at  constant  volume,  by  means  of  which  the 
well-known  manometric  method  of  determining  velocity  of  re- 
action could  be  applied.  Since  the  quantity  of  chemical  action 
produced,  even  by  relatively  large  quantities  of  emanation,  is 
small,  it  was  necessary  to  confine  the  reacting  substances  in 
volumes  so  small  (1  to  4  cm.^)  that  the  pressure  changes  could 
be  readily  measured.  Although  the  employment  of  such  small 
volumes  appears  disadvantageous  from  the  standpoint  of  the  full 
utilization  of  the  a  rays,  the  practice  is  not  only  justified  by  the 
accuracy  of  the  measurement  of  the  pressure  changes,  but  also 
presents  an  additional  simplification  if  one  wishes  to  calculate 
the  ionization  produced  in  the  gases   (see  Chapter  8). 

The  apparatus  used  by  Cameron  and  Ramsay  is  shown  in 
Figs.  3  and  3a.  The  introduction  of  emanation  into  the  reaction 
chamber  K  is  effected  by  means  of  the  Ramsay  gas  pipette  A.^ 

*T.  II.  Learning,  II.  Schlundt,  and  J.  E.  Underwood,  Tr.  Amer.  Electro- 
chem.  Soc.  30,  305    (1910). 

"A.  T.  Cameron  and  Wm.  Ramsay,  Journ.  Chem.  Soc.  Lond.  91i,  931; 
91ii,  1200 ;  1593 ;  92„  900  ;  992. 

•Wm.  Ramsay,  Proc.  Roy.  Soc.  70A,  113  (1905)  ;  Trans.  91,  939  (1907). 


REACTIONS  PRODUCED  BY  RADIUM  EMANATION 


67 


Fig.   3. 


68  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 


The  emanation  together  with -the  hydrogen  and  oxygen  resulting 
from  the  decomposition  of  the  original  radium  salt  solution  were 
collected  in  vessel  C,  where  the  hydrogen  and  oxygen  were  re- 
moved by  means  of  the  spark  gap  D.  After  exhausting  all  the 
apparatus  above  the  stopcock  B  through  F,  the  emanation  and 


A 

Of 


c 


i 


^ 


Fia.  4. — Various  Reaction  Vessels  op  Cameron  and  Ramsay. 
A.  Decomposition  of  HCl,  P,  Hg  cup ;  B.  combination  of  Hg  and  Og  (dry)  ;   0.  com- 
bination of  H2  and  O2  (moist)  ;  D.  decomposition  of  water. 

residual  gases  were  allowed  to  pass  through  the  P2O5  drying 
bulb  G  into  K.  Any  gas  or  gaseous  mixture  to  be  investigated 
was  introduced  into  the  reaction  chamber  in  the  same  way,  be- 
fore the  introduction  of  emanation. 


REACTIONS  PRODUCED  BY  RADIUM  EMANATION 


69 


TABLE  III 

Results  of  Cameron  and  Ramsay  on  the  Decomposition  of  Water 

by  Emanation 

Reaction:   (2H2O)  =  2H2  +  O^.    Water  Vol.  =  2.302  c.c. 
Gas  Vol.  =  3.789  c.c.    Ra  Em.  z=  31  milli-curies 


Days 

Pr.  in  mm. 

Vol.  in  c.c. 

Voo-Vt 

\oO-.Vo 

% 
Ra  Em  left 

0.0 

39.9 

0.200 

0.390 

100.0 

100.0 

0.25 

42.5 

0.212 

0.378 

96.9 

95.6 

0.81 

49.7 

0.248 

0.342 

87.7 

86.4 

0.92 

52.6 

0.262 

0.328 

84.1 

84.8 

1.89 

62.8 

0.310 

0.280 

71.8 

71.4 

2.80 

71.8 

0.358 

0.232 

59.5 

60.5 

3.81 

80.5 

0.401 

0.189 

48.5 

50.6 

4.81 

86.4 

0.431 

0.159 

40.8 

42.2 

5.81 

90.4 

0.451 

0.139 

35.6 

35.2 

6.81 

90.7 

0.484 

0.106 

27.2 

29.5 

10.07 

107.9 

0.538 
(0.590) 

0.052 

13.3 
0.0 

16.4 

The  experimental  arrangement  for  the  measurement  of  the 
decomposition  of  water  is  shown  in  Fig.  3a.  The  water  was  in- 
troduced immediately  over  the  mercury.  In  order  to  measure 
several  different  reactions  with  the  same  manometer,  the  arrange- 
ment shown  in  Fig.  4  was  employed,  in  which  the  special  uses 
of  the  various  reaction  vessels  are  indicated.  Vessel  D  (Fig. 
4)  was  the  form  finally  adopted  for  the  decomposition  of  water. 

In  Table  III  will  be  found  the  data  of  Cameron  and  Ramsay's 
Expt.  3  {loc.  cit.,  p.  973)  for  the  decomposition  of  water  in 
the  apparatus  shown  in  Fig.  4. 

Voo,  Vt  and  Vo  are  the  final,  intermediate,  and  initial  vol- 
umes respectively.    The  fraction  100  ^ ^  is  the  percentage  of 

V  00-Vo 

uncompleted  reaction  at  any  time  t.  The  last  column  shows  the 
percentage  of  emanation  remaining  at  the  corresponding  times. 
The  last  two  columns  are  in  approximate  agreement,  from  which 
Cameron  and  Ramsay  deduced  the  general  law  that  the  rate  of 
reaction  is  always  proportional  to  the  quantity  of  emanation  pres- 
ent.   It  follows  that  half  of  the  reaction  must  be  completed  in 


70  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

the  half  period  of  emanation,  which  is  3.85  days.  Cameron  and 
Ramsay  found  the  average  value  of  the  time  required  to  half 
complete  the  reaction  in  seven  different  experiments,  two  for  the 
decomposition  of  water  and  five  for  the  combination  of  hydro- 
gen and  oxygen,  to  be  3.86  days.  The  law  that  the  rate  of  re- 
action is  proportional  to  the  quantity  of  emanation  and  dimin- 
ishes at  the  same  rate  with  its  decay  can  be  accepted  for  a  liquid 
system,  as  in  the  decomposition  of  water,  but  in  a  gaseous  sys- 
tem in  which  the  pressure  changes,  it  no  longer  holds  except  in 
special  cases,  as  will  be  shown  in  Chapter  8.  The  conclusion  of 
Cameron  and  Ramsay  that  "each  atom  of  emanation  as  it  dis- 
integrates produces  the  same  amount  of  chemical  action"  is  also 
subject  to  some  modifications.  The  disintegration  is  effective 
in  producing  chemical  action  only  through  the  accompanying 
emission  of  an  a  particle.  The  amount  of  reaction  brought  about 
by  each  particle  will  depend  upon  the  length  of  its  path  in  the 
gas  phase,  which  will  evidently  vary  for  different  particles  from 
zero  up  to  the  longest  path  possible  in  a  given  vessel,  or  in  large^ 
vessels  would  be  limited  by  the  range  of  a  particles  in  the  gas. 

In  Table  IV  will  be  found  the  data  from  Cameron  and  Ram- 
say's Expt.  4  {loc.  cit.,  p.  974)  for  the  combination  of  hydrogen 
and  oxygen  in  the  moist  gases. 

By  comparison  of  the  last  two  columns  it  will  be  observed 
that  the  rate  of  chemical  action  shows  a  decided  tendency 
to  exceed  the  rate  of  decay  of  emanation.  This  means  that  the 
utilization  of  the  a  rays  becomes  less  complete  as  the  reaction 
proceeds,  owing  to  the  reduction  in  pressure  and  consequent 
diminution  in  the  number  of  molecules  encountered  by  each 
particle.  Later  (see  Table  XI),  cases  will  be  given  where  larger 
quantities  of  emanation  are  used  so  that  the  gas  pressure  changes 
through  much  wider  limits,  and  the  discrepancy  becomes  much 
more  pronounced,  showing  that  Cameron  and  Ramsay's  law  is 
a  special  case,  applying  in  gases,  only  when  the  pressure  change 
is  slight.  This  can  be  illustrated  further  by  comparison  of  the 
last  two  columns  in  Table  V,  in  which  the  amount  of  emanation 
used  is  smaller  than  in  Table  IV,  consequently  the  relative  pres- 
sure change  is  less  and  the  agreement  between  per  cent  of  reaction 
and  of  emanation  decayed  is  almost  as  good  as  in  the  case  for  de- 
composition of  water  (Table  III). 

In  the  experiments  just  reported  with  moist  gas,  the  plain 


REACTIONS  PRODUCED  BY  RADIUM  EMANATION 


71 


TABLE  IV 

Results  of  Cameron  and  Ramsay  on  the  Formation  of  Water  by 
Emanation  (Moist) 

Volume  of  Tube  2.186  c.c.    Ra  Em.  46.5  milli-curies. 
Reaction  2H2  +  02=  (2H2O) 


Days 

Pr.  in  mm. 

Vol.  in  c.c. 

Vt-Voo 

Vo-Voo 

Ra  Em  left 

0.0 

523.5 

1.505 

0.668 

100.0 

100.0 

1.02 

487.0 

1.401 

0.564 

84.4 

83.2 

2.07 

442.0 

1.271 

0.434 

65.0 

68.9 

3.07 

405.6 

1.167 

0.330 

49.4 

57.6 

4.13 

384.5 

1.106 

0.269 

40.3 

47.6 

4.99 

369.5 

1.063 

0.226 

33.8 

40.7 

6.11 

352.2 

1.013 

0.176 

26.3 

32.3 

7.07 

343.5 

0.988 

0.151 

22.6 

28.0 

9.11 

321.4 

0.924 

0.087 

13.0 

19.4 

10.16 

319.3 

0.919 

0.082 

12.3 

16.1 

11.04 

316.6 

0.911 

0.074 

11.1 

13.7 

12.10 

312.3 

0.898 

0.061 

9.1 

11.4 

97.0 

291.0 

0.837 

0.0 

0.0 

0.0 

form  of  tube  (Fig.  3a,  p.  67)  was  used.  In  Table  V  are  the 
results  of  Cameron  and  Ramsay  for  dry  hydrogen  and  oxygen, 
using  the  form  B,  Fig.  4,  in  which,  part  of  the  tube  was  filled 
with  P2O5.  No  difference  was  observed  by  Cameron  and  Ram- 
say in  the  action  of  emanation  on  dry  or  on  moist  hydrogen  and 
oxygen.    This  has  also  been  confirmed  by  Lind.'' 

Cameron  and  Ramsay  {loc.  cit.)  also  measured  by  the  same 
method  the  effect  of  radium  emanation  in  decomposing 
CO2,  CO,  NH3,  and  HCl  gases  and  in  synthesizing  NHg  from  its 
elements.  The  data  for  some  of  these  reactions  will  be  pre- 
sented in  Table  X,  §  42,  in  a  somewhat  different  connection. 

Before  passing  to  other  experiments  it  should  be  mentioned 
that  Cameron  and  Ramsay  regarded  their  work  as  preliminary  in 
nature  and  it  has  since  been  shown  ^  that  the  quantities  of  ema- 
nation reported  by  them  were  probably  higher  than  the  quanti- 

TS.  C.  Lind,  Journ.  Amcr.  Chem.  Soc.  1,1,  540  (1919). 
8S.  C.  Lind,  ihid.  41,  p.  534  and  pp.  549-50   (1919). 


72  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

TABLE  V 

Results  of  Cameron  and  Ramsay  on  the  Formation  of  Water  by 
Emanation  (Dry) 

Reaction:  2H2  +  02=  (2H2O) 

Expt.  6  iloc.  cit,  p.  977).    Vol.  of  Tube  4.996  c.c. 

Ra  Em.  22.0  milli-curies. 


Days 

Pr.  in  mm. 

Vol.  in  c.c. 

Vt-Voo 

'<'1- 

% 
Ra  Em  left 

0.0 

577.6 

3.798 

0.555 

100.0 

100.0 

1.07 

564.1 

3.709 

0.466 

84.0 

82.6 

1.96 

552.4 

3.631 

0.388 

69.9 

70.3 

2.84 

546.9 

3.595 

0.352 

63.4 

60.0 

3.80 

535.6 

3.522 

0.279 

50.3 

50.5 

4.80 

530.2 

3.485 

0.242 

43.6 

42.2 

6.80 

521.5 

3.428 

0.185 

33.3 

29.5 

9.88 

505.6 

3.324 

0.081 

14.6 

16.9 

11.91 

502.8 

3.305 

0.062 

11.2 

11.8 

13.90 

496.4 

3.264 

0.021 

3.8 

8.3 

21.89 

493.3 

3.243 

0.0 

0.0 

1.9 

ties  actually  present  (§  44).  Nevertheless  their  pioneer  work  is 
of  great  interest  on  account  of  its  scope  and  methods,  and  repre- 
sents the  first  serious  attempt  to  deal  experimentally  with  this 
very  interesting  subject. 


31.    Experiments  of  Usher  on  the  Ammonia  Equilibrium. 

In  1910  Usher,'^  working  in  the  laboratory  of  Ramsay,  made 
an  exhaustive  study  of  the  decomposition  and  formation  of 
ammonia  by  radium  emanation.  He  definitely  stated,  what 
Cameron  and  Ramsay  had  already  considered  as  possible,  that 
the  a  particles  are  the  real  agents  of  the  reaction,  and  made 
the  very  important  advance  in  recognizing  clearly  that  increase 
of  volume  will  increase  the  amount  of  chemical  action  produced 
by  a  given  quantity  of  emanation  through  the  lengthening  of  the 
effective  paths  of  the  a  rays.  Usher  calculated  that  the  average 
number  of  molecules  decomposed  by  each  a  particle  in  a  large 

»F.  L.  Ushor,  Journ.  Chcm.  Soc.  Lond.  97,,  389-405  (1910). 


REACTIONS  PRODUCED  BY  RADIUM  EMANATION  73 

volume  (2  liters)  was  134,000,  which  he  estimated  to  be  90%  of 
the  maximum,  were  all  the  a  particles  wholly  effective.  Through 
considerations  involving  ionization  Lind  ^^  used  Usher's  data  in 
calculating  the  maximum  number  of  NH3  molecules  that  would 
be  decomposed  by  a  single  a  particle  to  be  274,000.  From  more 
recent  experiments  of  Wourtzel  ^^  it  appears  that  the  number  at 
ordinary  temperature  must  be  at  least  388,000.  The  higher  effi- 
ciency found  by  Wourtzel  for  the  decomposition  of  NH3  by  ema- 
nation appears  to  raise  some  doubt  as  to  the  quantity  of  emana- 
tion reported  by  Usher,  similar  to  the  discrepancies  attaching 
to  the  data  of  Cameron  and  Ramsay  (§  §  30  and  44). 

With  respect  to  the  reverse  reaction,  the  formation  of  NH3 
from  its  elements.  Usher  found  a  reduction  in  pressure,  as  had 
Cameron  and  Ramsay,  but  on  analyzing  the  gaseous  products, 
failed  to  find  any  certain  quantity  of  NH3,  and  concluded  that 
the  reduction  of  pressure  was  due  to  some  other  cause,  possibly 
to  the  removal  of  hydrogen  by  being  driven  into  the  glass  walls 
by  the  a  particles.  According  to  Usher,  therefore,  the  equilibrium 
2NH3  ^  No  +  3H2,  in  the  presence  of  radium  emanation  at  ordi- 
nary temperature,  fies  practically  wholly  on  the  side  of  decompo- 
sition of  NH3. 

'OS.  C.  Lind,  Joum.  Phys.  Chem.  IG,  603  (1912). 
"E.  E.  Wourtzel,  Le  Radium  11,  342   (1919). 


Chapter  7. 

Eelation  Between  Gaseous  Ionization  and  Radio- 
chemical Effects. 

32.    Historical  Development  of  the  Ionization  Theory  of  the 
Chemical  Effects  of  Corpuscular  Radiation. 

In  the  foregoing  chapters  the  chemical  effects  of  the  radia- 
tions, particularly  of  the  a  rays,  of  radium  have  been  considered, 
first  in  their  qualitative  and  then  in  their  quantitative  relation- 
ships. The  quantitative  character  of  the  investigations  has  ex- 
tended to  the  measurement  of  the  chemical  change  produced,  and 
included  a  certain  knowledge  of  the  quantity  of  radioactive  ma- 
terial causing  the  change.  As  has  already  been  pointed  out, 
this  knowledge,  though  important  and  quite  as  far-reaching  as 
that  possessed  in  some  other  branches  of  radiochemistry,  fur- 
nishes little  information  as  to  the  true  relation  between  quantity 
of  radiation  and  chemical  change,  since  the  actual  quantity  of 
the  former  utilized  in  bringing  about  the  latter  was  known  only 
very  approximately,  on  account  of  losses  of  radiation  to  the 
walls  of  the  vessel  and  other  losses  difficult  to  take  into  account. 
These  difficulties  are  no  greater  than  are  met  in  dealing  with 
other  forms  of  radiation,  and  under  experimental  conditions  prop- 
erly controlled,  the  difficulties  are  much  less  with  a  radiation 
from  radium  emanation  than  with  other  forms  of  radiant  energy. 

Very  definite  laws  have  been  established  (Chapter  2)  for  the 
absorption  of  a  rays  in  gases  by  means  of  a  study  of  the  ioniza- 
tion produced.  As  will  be  shown  in  the  present  chapter,  it  has 
proved  very  instructive  to  relate  statistically  the  ionization  in  a 
given  system  to  the  chemical  action.  It  is  perhaps  a  matter 
of  surprise  that  such  comparisons  were  not  made  earlier  than 
was  the  case.  It  will  not  be  without  interest  to  point  out  some 
of  the  reasons  historically.  Of  course,  no  such  comparisons  were 
possible  before  the  development  of  the  standards  and  methods  of 
measurement  of  the  radioactive  substances  involved.     And  in 

74 


IONIZATION  AND  RADIOCHEMICAL  EFFECTS  75 

the  case  of  radium  emanation,  its  collection  and  purification  are 
prerequisites.  A  knowledge  of  the  ionization  in  air  and  in  other 
gases  and  of  the  distribution  of  that  ionization  along  the  path 
of  the  radiant  particles  was  also  essential.  The  chief  draw- 
back lay  in  the  fact  that  the  ionization  was  determined  for  gas- 
eous systems,  whereas  the  chemical  actions  were  first  carried  out 
quantitatively  in  liquid  systems,  and  a  comparison  appeared  too 
indirect  to  have  value.  Furthermore,  the  gas  reactions  which 
were  studied  quantitatively  were  not  carried  out  under  condi- 
tions from  which  the  ionization  could  be  readily  estimated. 

In  1907  Bragg  ^  first  calculated  from  data  of  Ramsay  and 
Soddy  2  that  the  number  of  molecules  of  water  decomposed  was 
almost  exactly  equal  to  the  number  of  ions  that  would  have  been 
produced  in  air  by  the  emanation  employed.  Apparently  Bragg 
was  not  impressed  by  the  equality  he  found  and  referred  to  it  as 
a  "curious  parallelism  in  numbers."  Mme.  Curie  ^  stated  in  1910 
with  respect  to  the  decomposition  of  water  by  a  particles  that, 
"the  production  of  electrolytic  gas  by  radium  in  solution  is  of 
the  same  order  of  magnitude  as  that  which  one  would  obtain 
if  the  number  of  molecules  of  water  decomposed  by  the  a  rays 
emitted,  were  equal  to  the  number  of  ions  which  these  same 
rays  would  produce  in  air." 

In  1910  Le  Blanc  calculated  from  Bergwitz's^^  data  on  the 
decomposition  of  water  by  polonium,  that  the  saturation  current 
in  air  measured  by  Bergwitz  for  the  a  radiation,  corresponded 
very  closely  to  the  current  that  would  be  required  by  Faraday's 
law  to  decompose  the  same  amount  of  water  electrolytically  as 
was  decomposed  by  the  a  radiation  of  polonium.  While  Le  Blanc's 
calculation  suffers  from  the  disadvantage  of  comparing  air  ioni- 
zation with  water  decomposition,  yet  the  recognition  of  the  ap- 
plicability of  Faraday's  law  to  this  class  of  reactions,  which  Le 
Blanc  very  aptly  classifies  under  "electrolysis  without  elec- 
trodes," is  of  great  importance,  and  it  is  unfortunate  that  it 
was  not  given  greater  prominence  than  scant  mention  in  his 
Elektrochemie   (5th  Ed.,  p.  317).     Later  Le  Blanc*  published 

»W.  H.  Bragg,  Phil.  Mag.    (6)    13,  333    (1907). 

«W.  Ramsay  and  F.  Soddy,  Proc.  Roy.  Soc,  72,  204  (1903). 

"Mme.  Curie,  "Traits  de  Radioactivity,"  Vol.  II,  pp.  247-8   (1910). 

3a  K.  Bergwitz,  Phys.  Zeit.  II,  273-5   (1910). 

*M.  Le  Blanc,  Zeit.  Phys.  Chem.  85,  511   (1913). 


76  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

in  full  his  calculations  from  Bergwitz's  data  on  which  his  state- 
ment was  founded. 

33.    Production  of  Ozone  by  a  Particles. 

In  1911  the  writer^  undertook  in  the  Institut  fUr  Radium- 
forschung  in  Vienna,  by  measuring  the  quantity  of  ozone  formed 
by  the  action  of  a  rays  of  radium  emanation  on  gaseous  oxygen, 
to  compare  the  chemical  action  with  the  ionization.  Instead  of 
adopting  the  method  of  Cameron  and  Ramsay  of  mixing  emana- 
tion directly  with  the  gas,  purified  emanation  was  introduced  into 
an  extremely  thin-walled  small  glass  sphere  about  1  mm.  in  diam- 
eter. The  wall  thickness  was  of  the  order  0.005  mm.  which  would 
be  equivalent  to  about  1  cm.  of  air  in  the  absorption  of  a  rays, 
leaving  the  a  rays  from  Ra  C  a  free  path  outside  the  bulb  of 
about  6  cms.  By  placing  a  bulb  of  this  kind  at  the  center  of 
a  glass  sphere  of  about  12  cms.  diameter  filled  with  oxygen,  the 
free  path  of  the  a  rays  is  fully  utilized  without  their  reaching 
the  wall.  The  ozone  formed  was  absorbed  in  neutral  KI  solution 
and  measured  chemically. 

The  construction  of  such  thin  a  ray  bulbs  can  not  be  under- 
taken by  the  ordinary  glass-blower  and  will  therefore  be  de- 
scribed in  some  detail.  The  first  glass  vessels  thin  enough  to 
transmit  a  rays  were  used  by  Rutherford  and  Royds  ^  in  their 
work  on  the  nature  of  the  a  particle.  They  were  thin-walled 
capillary  tubes,  but  since  no  details  of  their  construction  were 
given,  the  method  of  making  the  thin  bulbs  was  worked  out 
more  or  less  independently  by  Duane  and  Lind  in  the  laboratory 
of  Mme,  Curie.  Thin-walled  soft  glass  tubing  of  8-10  mm.  di- 
ameter is  first  drawn  down  in  the  free  blast  flame  to  a  diameter 
of  about  1  mm.  over  a  length  of  6-8  inches.  One  end  is  then 
sealed  and  the  other  attached  to  an  ordinary  foot-bellows  or 
other  source  of  pressure.  Further  manipulation  is  carried  on  in 
a  simple  furnace  consisting  of  a  six  inch  length  of  hard  glass  or 
quartz  tubing  of  about  %  inch  internal  diameter  open  at  both 
ends.  The  middle  portion  of  the  tube  furnace  is  heated  either 
with  a  blast  lamp,  or  in  the  case  of  quartz  with  a  flame  contain- 
ing some  oxygen,  and  should  be  provided  with  an  asbestos  hous- 

»S.  C.  Lind,  Sitzb.  Akad.  Wisa.  Wien  Ila,  120,  1709   (1911)  ;  Monatah.  32, 
295.     Amer.  Chem.  Journ.,  47,  397-415   (1912)  ;  Lc  Radium  9,  104-G   (1912). 
•E.  E.  Rutherford  and  T.  Royds,  Phil.  Mag.  (6)  17.  2S1  (1909). 


i 


IONIZATION  AND  RADIOCHEMICAL  EFFECTS  77 

ing  to  retain  the  heat.  The  glass  tube  to  be  worked  is  then 
inserted  entirely  through  the  furnace  and  held  by  the  two  project- 
ing ends.  The  lower  temperature  of  the  furnace,  as  compared 
with  a  free  flame,  is  compensated  by  the  higher  pressure  used  in 
working  the  glass.  Under  a  suitable  pressure  the  soft  tubing 
is  further  drawn  out  until  it  tapers  to  a  very  fine  tip  which  is 
broken  off  at  the  thinnest  point  capable  of  being  worked.  The 
tip  is  sealed  off  without  the  collection  of  excess  glass  by  just 
touching  the  edge  of  a  very  small  flame.  The  tip  is  then  intro- 
duced into  the  hottest  zone  of  the  furnace  and  while  blowing 
strongly  into  the  tube,  the  expansion  of  a  small  bulb  on  the  end 
can  be  observed  from  the  open  end  of  the  furnace.  The  bulb 
must  be  withdrawn  just  at  the  right  moment  to  prevent  its 
blowing  out.  With  some  practice,  bulbs  with  walls  equivalent 
to  1  cm.  of  air  for  a  ray  absorption  can  be  constructed  which 
will  withstand  atmospheric  pressure  in  either  direction.  The 
bulb  may  then  be  sealed  to  any  glass  apparatus  by  means  of 
the  original  stem,  which  should  be  provided  with  an  in-sealed 
platinum  wire  to  conduct  away  the  unipolar  charge  if  it  is  de- 
sired to  enclose  a  large  quantity  of  emanation  entirely  in  glass 
over  mercury. 

The  emanation  confined  in  such  a  bulb  can  be  determined 
after  four  hours  by  its  y  radiation  iu  the  usual  way.'^  A  radio- 
metric method  was  devised"  by  Lind  {loc.  cit.)  for  determining 
the  maximum  range  of  the  a  particles  from  Ra  C  outside  the  bulb. 
It  consists  in  placing  the  bulb  at  several  known  distances  above 
a  large  ZnS  screen  in  an  absolutely  dark  room  and  measuring  the 
diameters  of  the  circles  of  light  produced  on  the  screen  at  differ- 
ent distances.  In  all  cases  the  range  sought  is  the  distance  from 
the  bulb  to  the  outer  edge  of  the  light  circle,  which  is  the  hypoth- 
enuse  of  a  right  triangle  of  which  the  vertical  distance  from 
the  screen  and  the  radius  of  the  light  circle  are  the  other  two 

diam  ^ 
sides.    From  the  relation:     Range^  —  — j-^  +  dist.^,  the  range 

can  be  calculated  independently  at  several  different  distances, 
and  should  agree  in  all  cases.  The  accompanying  Table  VI 
gives  the  results  of  a  series  of  such  measurements  on  a  tube  of 
about  0.005  mm.  wall  thickness. 

'^Rutherford,  "Radioactive  Substances,"  Appendix  A,  p.  657  (1913).  Ma- 
kower  and  Geiger,  "Practical  Measurements  in  Radioactivity,"  p.  106  (1912). 
S.  C.  Lind,  Joum.  Indus.  Eng.  Chem.,  12,  472   (1920). 


78  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 


TABLE  VI 

Radiometric  Measurement  of  the  Free  Range  of  a  Particles  from 
Ra  C  Outside  a  Thin-walled  a  Ray  Bulb 


Dist.  from  Screen 

Diameter 
of  Light  Circle 

Max.  Range 

cms. 

cms. 

cms. 

5.8 

2.5 

5.9 

5.4 

5.0 

5.9 

5.0 

6.4 

5.9 

4.5 

7.3 

5.8 

4.1 

8.5 

5.9 

3.3 

10.0 

6.0 

Average 

5.90  dz  0.03  cm. 

Before  undertaking  measurements  depending  on  such  feeble 
luminosity  the  eye  should  be  rested  for  thirty  minutes  in  the 
dark.  Readings  should  be  made  with  a  feeble  ruby  light.  The 
diameter  of  the  light  circle  is  most  conveniently  determined  by 
using  steel  calipers  with  sharp  points  which  can  be  used  to 
scratch  the  surface  of  the  ZnS,  producing  a  momentary  spark 
which  serves  to  locate  the  boundaries  of  the  light  circle. 

The  object  of  obtaining  the  air  range  of  a  rays  outside  the 
bulb  is  to  enable  the  calculation  of  the  ionization  produced  in 
the  oxygen.  The  quantities  of  emanation  employed  in  the  ozoni- 
zation,  25  to  60  millicuries,  produce  an  ionization  far  too  intense 
to  be  measured  by  the  saturation  current  method  (§  15).  By 
referring  to  the  range  of  a  rays  from  emanation  and  Ra  A 
(Table  I)  and  to  the  ionization  produced  by  them  and  by  Ra  C 
along  their  paths  (Fig.  1),  and  correcting  for  the  specific  ioniza- 
tion of  oxygen  compared  with  air  (Table  II) ,  the  total  ionization 
can  be  calculated.  One  additional  correction,  however,  is  neces- 
sary, since  the  a  particles  pass  through  the  thin  glass  wall  at 
all  possible  angles,  one  must  correct  for  the  obliquity  of  inci- 
dence.   This  was  done  by  a  graphical  method. 

The  total  number  of  a  particles  emitted  by  a  certain  initial 
quantity  of  emanation  through  a  given  time  interval  may  be 
calculated  in  two  slightly  different  ways,  both  mathematically 


IONIZATION  AND  RADIOCHEMICAL  EFFECTS  79 

identical  in  principle.  The  average  effective  emanation  E  over 
a  time  interval  t  is:  E=^    °       ^^'in  which  Et  may  be  found  at 

any  time  t  by  consulting  the  Kolowrat  Table  (Appendix,  Table 
A),  and  I  is  the  decay  constant  for  radium  emanation  equal  to 
0.0075  hr-i  or  0.1800  day^  The  average  value  E  in  terms  of 
curies  then  need  only  be  multiplied  by  the  total  number  of  sec- 
onds and  by  the  number  of  a  particles  emitted  per  second,  origi- 
nally measured  as  3.4x10^^  in  terms  of  the  Rutherford  radium 
standard,  which  becomes  in  terms  of  the  International  standard 
3.57x10^^,  or  for  all  three  sets,  including  emanation  and  Ra  A 
and  C  10.71x10^°  a  particles  per  second.  Hess  and  Lawson  ®  have 
recently  determined  a  higher  value  3.72x10^°,  which  has  been 
adopted  for  all  calculations  in  the  present  work. 

The  more  direct  method  of  calculating  the  total  number 
emitted  is  to  take  into  account  the  quantity  of  emanation  de- 
caying in  the  given  time  interval  by  reference  to  the  Kolowrat 
table,  and  multiplying  the  quantity  by  the  total  number  of  par- 
ticles emitted  by  1  curie  of  emanation  in  its  complete  disintegra- 
tion, 1.78x10^®  for  a  single  set  of  a  particles,  according  to  Hess 
and  Lawson.  For  three  sets  (emanation  in  equilibrium) :  Total 
a  =  5.34xlO^«.Eo(l-e-^t). 

The  purification  of  the  emanation  used  was  by  a  chemical 
method  developed  in  the  Curie  laboratory  consisting  in  the  re- 
moval of  hydrogen  and  oxygen  by  means  of  copper  and  copper 
oxide  heated  externally  in  the  glass  tube  leading  from  the  radium 
solution  to  the  small  bulb.  In  the  same  way  organic  gases  com- 
ing from  stopcock  grease  were  oxidized  by  passing  over  hot 
KgCrgO^  (or  better  PbCr207),  the  products  of  the  two  combus- 
tions being  absorbed  by  P2O5  and  fused  KOH  (or  soda  lime). 
Final  purification  was  made  by  freezing  the  emanation  in  a  side 
tube  immersed  in  liquid  air  while  pumping  off  the  residual  gases. 
The  emanation  is  finally  confined  by  mercury  in  the  small  a  ray 
bulb  so  as  just  to  fill  it.  From  radiation  considerations  it  is 
essential  that  the  mercury  shall  stand  at  all  times  just  at  the 
neck  of  the  thin  bulb.  In  using  the  same  apparatus  for  the 
combination  of  hydrogen  and  chlorine  (see  p.  119)  H.  S.  Taylor® 
has  added  a  very  ingenious  regulator  to  insure  this  condition. 

"V.  F.  Hess  and  R.  W.  Lawson,  Sitzl).  Akad.  Wiss.  Wien  Ila,  127,  405-57 
»II.  S.  Taylor,  Joum.  Amer.  Chem.  Soc.  37,  24-38  (1915). 


80  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

The  quantities  of  ozone  found  in  the  different  experiments 
were  not  concordant,  but  it  was  very  apparent  that  the  order 
of  magnitude  of  the  total  number  of  ions  and  of  ozone  molecules 
is  the  same.  The  experiment  in  which  the  maximum  quantity  of 
ozone  was  determined  was  one  in  which  the  average  emanation 
was  58.5  milli-curies  acting  over  5.0x10*  sees,  in  which  time 
8.4x10^^  a  particles  were  emitted  producing  2.6x10^^  pairs  of  ions, 
and  1.4x10^®  molecules  of  O3.  Using  the  more  recent  data  of 
Hess  and  Lawson  for  the  number  of  a  particles  emitted,  the  ioni- 
zation becomes  2.8x10^®,  and  the  ratio  of  the  number  of  pairs  of 
ions  (N)  to  the  number  of  ozone  molecules  (M)  is  exactly  2.0, 
which  would  be  required  according  to  Faraday's  law  for  the  for- 
mation of  ozone  electrolytically.  The  justification  for  giving 
most  weight  to  the  experiment  in  which  the  maximum  quantity 
of  ozone  was  found  lies  in  the  fact  that  the  lower  values  were 
probably  due  to  losses  before  chemical  measurement,  perhaps 
through  traces  of  mercury  in  the  ozonizing  chamber.  This  ex- 
periment in  the  ozonization  of  oxygen  constituted  the  first  direct 
comparison  of  ionization  and  chemical  effect  where  both  were 
referred  to  the  same  gaseous  system.  A  strong  confirmation  of 
the  result  is  furnished  by  the  work  of  Kriiger,^®  who  studied  the 
formation  of  ozone  by  electronic  discharge  (Lenard  rays)  and 
obtained  results  similar  to  those  for  a  rays,  drawing  the  conclu- 
sion, however,  that  one  pair  of  ions  is  involved  in  the  formation 
of  each  ozone  molecule. 

The  formation  of  ozone  outside  a  thin  a  ray  bulb  containing 
even  a  few  millicuries  of  emanation  is  continuously  perceptible 
by  its  odor.  The  same  is  true  in  the  immediate  neighborhood  of 
a  strong  radium  preparation  or  any  other  source  of  intense  a  ra- 
diation. From  the  results  reported  in  the  foregoing  parts  of  this 
paragraph,  it  appears  fairly  certain  that  ozonization  by  a  radia- 
tion and  by  electronic  discharge  is  an  electrical  process  inti- 
mately connected  with  ionization  of  oxygen.  Present  data  are 
hardly  sufficient  to  establish  the  exact  mechanism  of  the  reaction, 
although  a  number  of  attempts  have  been  made  in  this  direc- 
tion. It  is  not  necessary  that  the  electrical  quantities  involved 
should  be  the  same  as  in  electrolysis,  since  the  work  of  J.  J. 

'OF.  KrUger,  Php9.  Zeit.,  13,  1040-3  (1912)  ;  Normt  FeatachHft,  pp.  240-51 
(J012). 


IONIZATION  AND  RADIOCHEMICAL  EFFECTS  81 

Thomson  ^^  has  shown  that  the  varieties  of  gaseous  oxygen  ions 
is  much  greater  than  those  known  in  solution.  It  would  be  some- 
what simpler  to  propose  a  theory  on  the  basis  of  one  molecule 
of  ozone  per  each  pair  of  ions,  than  for  two  pairs,  and  as  Milli- 
kan,  Gottschalk  and  Kelly  ^^  have  shown,  the  ionization  of  some 
common  gases,  including  oxygen,  by  a  rays  results  in  the  removal 
of  but  one  electron  from  a  molecule.  The  writer  ^^  proposed  a 
very  general  theory  based  upon  the  formation  of  cluster  ions 
around  a  charged  atom  or  molecule,  which  upon  being  electrically 
neutralized  would  break  down  to  the  highest  stable  polymer,  in 
the  case  of  oxygen,  ozone.  Recent  work  of  Loeb  ^*  and  of  Wel- 
lisch  ^^  has  cast  doubt  upon  the  existence  of  such  cluster  ions.^^ 
Various  possible  mechanisms  for  the  formation  of  ozone  have 
been  formulated  by  Strong  ^^  and  by  Rideal  and  Kunz.^^  The 
present  experimental  evidence  hardly  appears  sufficiently  exact 
to  decide  in  favor  of  any  particular  theory.  Wendt  and  Lan- 
dauer  ^®  have  discussed  fully  the  possibilities  in  connection  with 
the  formation  of  triatomic  hydrogen. 

34.    Other  Gas  Reactions. 

The  apparently  close  relation  between  gaseous  ionization  and 
ozone  formation  rendered  it  very  desirable  to  see  if  a  similar  rela- 
tion holds  for  other  gas  reactions  produced  by  a  radiation.  The 
extensive  data  of  Cameron  and  Ramsay  were  available  for  the 
comparison  provided  a  method  could  be  devised  of  calculating 
the  effective  ionization  in  the  vessels  used.  Since  the  volumes 
used  were  very  small  the  a  particles  in  all  cases  completely  trav- 
ersed the  gas  space,  and  in  most  cases  the  paths  would  be  lim- 
ited to  the  first  one  or  two  centimeters  from  the  point  of  origin, 
in  which  the  ionization  remains  constant  along  the  path,  which 
presented  an  additional  simplification.    The  problem  seemed  to 

"J.  J.  Thomson,  "Rays  of  Positive  Electricity"  (1913).  Phil.  Mag.  (6) 
21,  239  (1911). 

12  R.  A.  Millikan,  V.  H.  Gottschalk  and  M.  J.  Kelly,  Phys.  Rev.  (2)  15, 
157    (1920). 

"  S.  C.  Lind,  Amer.  Chem.  Joum.,  47,  414   (1912). 

'*L.  B.  Loeb,  Phys.  Rev.    (2)    8,  633   (1916). 

"E.  M.  Wellisch,  J.  Franklin  Inst.  184,  775   (1917). 

'*G.  L.  Wendt  and  R.  S.  Landauer,  Joum.  Amer.  Chcm.  Soc.  Ji2,  944 
(1920). 

"W,  W,  Strong,  Amer.  Chcm.  Joum.  50,  100-31   (1913). 

"E.  K.  Rideal  and  J.  Kunz,  Joum.  Phys.  Chcm.,  24,  379-93  (1920). 


82  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

be  then  to  find  a  solution  for  the  average  path  proceeding  in  a 
straight  line  from  any  point  within  a  given  volume  or  any  point 
on  the  inner  surface  in  any  direction  until  again  encountering 
the  wall.  For  any  volumes  except  spherical  ones  the  mathe- 
matical problem  is  one  of  great  difficulty  as  will  be  seen  in  the 
following  section. 

35.     Calculation  of  the  Average  Path  of  a  Particles. 

In  1912  the  solution  of  this  problem  was  undertaken  by 
Lind  ^®  for  the  sphere.  It  was  established  that  the  average  path 
is  a  constant  fraction  of  the  radius  for  a  sphere  of  any  size. 
The  numerical  value  of  the  fraction  was  found  by  applying  the 
general  formula,  at  first  to  ten,  and  later  to  one  hundred  spheres 
dividing  the  spherical  volume  into  100  equal  parts.  A.  C.  Lunn  ^^ 
has  pointed  out  that  an  error  was  made  in  using  the  plane  in- 
stead of  the  solid  angle  (§)  Fig.  5.    The  expression  according  to 


Fig.   5. 

Lunn  for  a  sphere  is  the  following.  If  p  be  the  average  path 
for  all  a  particles  originating  at  any  point  P  within  the  sphere 
and  traveling  to  the  wall  in  a  straight  line  PA  at  any  solid  angle 
■0  with  the  line  PCB  through  the  center  of  the  sphere,  where  b  is 
any  given  distance  from  the  center,  and  ^i  is  the  ratio  b/r, 

y^'T  , 

[bcos  •»  +  r  V  1  —  bVr^  sin  2  <»]  sin  ^  d  d. 
o 

»S.  C.  Lind,  Journ.  Phys.   CJiem.,  16,  5G7    (1912). 

="<»  Private  communication  from  Prof.  A.  C.  Lunn,  Ryerson  Physical  Labora- 
tory, University  of  Chicago. 


IONIZATION  AND  RADIOCHEMICAL  EFFECTS  83 


p  =  l/2f  [bx  +  rV  (1  — bVr^)  (1  — x^)] 


dx. 


r    r         1  —  n^      1  +  ^^ 
Finally  for  given  b:  mean   p  =  —  -<  l-\ log V 

For  b  r=  1,  p  =  0.5r.  Lunn's  integral  for  the  whole  spherical 
volumes  gives:  p  =  0.75r.  Taking  into  account  that  in  small 
spheres  the  induced  activity  is  deposited  on  the  wall  and  there- 
fore the  a  particles  for  Ra  A  and  C  originate  from  the  wall,  half 
of  them  being  immediately  lost  in  the  wall,  while  the  radium 
emanation  is  distributed  as  gas  throughout  the  volume,  the  aver- 
age path  of  all  three  sets  of  a  particles  from  emanation  in  equilib- 
rium will  be:  p  =  1/3  (0.75  +  2  x  0.5) .  r  =  0.5833  r. 

For  volumes  other  than  spherical  the  problem  becomes  mathe- 
matically far  more  difficult.  From  the  use  of  graphical  methods 
the  writer  concluded  that  the  average  path  in  cylinders  in  which 
the  length  does  not  exceed  the  diameter  by  more  than  a  few  fold 
of  the  diameter  would  be  approximately  the  same  fraction  of 
the  radius  of  the  sphere  of  equal  volume  as  if  the  volume  were 
spherical.2^  In  all  future  work  it  will  be  advisable  to  use 
spherical  vessels  in  order  to  simplify  the  calculation  of  the  ioni- 
zation. Some  work  has  already  been  carried  out  in  spheres  by 
the  writer  which  is  reported  in  Chapters  8  and  9.  The  whole 
question  of  the  calculation  of  ionization  in  vessels  of  different 
shapes  and  sizes  is  one  worthy  of  further  research.  The  work  of 
Flamm  and  Mache  ^^  on  the  quantitative  measurement  of  emana- 
tion in  plate  condensers  with  guard-ring  has  a  bearing  upon  the 
subject,  but  is  not  directly  applicable  to  radiochemical  experi- 
ments. The  empirical  formula  of  Duane  and  Laborde  was 
given  in  §  29,  but  is  not  applicable  to  small  volumes. 

36.    Results  of  Various  Investigations. 

By  use  of  the  method  of  calculating  ionization  by  means 
of  the  average  path  of  the  a  particles  the  experiments  of  Cam- 

"■  Prof.  Lunn  is  extending  his  calculations  to  otlier  geometrical  forms  than 
the  sphere  and  is  convinced  that  the  average  path  in  cylinders  of  length  ten 
times  the  diameter  will  be  sufficiently  different  from  that  in  the  sphere  of  the 
same  volume  to  be  easily  tested  experimentally.  Prof.  L.  D.  Roberts  of  the 
Colorado  School  of  Mines  has  begun  an   experimental  test. 

22  L.  Flamm  and  H.  Mache,  Sitsh.  Akad.  Wiss.  Wien  Ila,  121,  227  (1912)  ; 
122,  535;  1539   (1913). 


84  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

eron  and  Ramsay  and  of  others  become  available  for  at  least 
an  approximate  comparison  of  the  electrical  and  chemical  ef- 
fects. Other  methods  more  or  less  indirect  have  been  devised  for 
attaining  the  same  end.  Duane  and  Scheuer  ^^  employed  large 
quantities  of  emanation  in  thin-walled  capillaries.  After  meas- 
urement of  the  chemical  effects  the  tubes  were  held  until  the 
emanation  had  died  to  such  a  low  value  that  saturation  current 
measurements  could  be  applied  even  to  the  a  radiation.  Cor- 
rection had  to  be  made  for  the  growth  of  polonium  during  this 
period  and  also  for  the  ionization  due  to  penetrating  radiation. 
Scheuer  2*  for  large  bulbs  used  the  empirical  formula  of  Duane 
and  Laborde^^  and  corrected  for  the  specific  ionization  of  the 
gases  employed.  Wourtzel  ^^  employed  still  another  method, 
extrapolating  from  smaller  volumes  up  to  those  at  which  absorp- 
tion and  ionization  reach  a  maximum,  in  order  to  use  the  value 
for  total  ionization  of  the  whole  a  particle  in  the  given  gas. 

At  the  end  of  this  paragraph  will  be  found  Table  VII,  in 
which  all  the  experimental  data  available  for  the  comparison  of 
chemical  effect  and  ionization  have  been  collected.  The  appli- 
cation of  the  "average  path"  method  to  the  results  of  Cameron 
and  Ramsay  is  not  strictly  accurate  on  account  of  the  departure 
of  the  volumes  from  the  spherical,  but  it  is  unlikely  that  the 
errors  thus  introduced  are  so  great  as  the  uncertainty  attaching 
to  the  quantities  of  radium  emanation  reported  in  the  earlier 
experiments.  Many  of  the  experiments  summarized  in  this  table 
will  be  given  detailed  consideration  in  subsequent  paragraphs 
(see  accompanying  cross-references) .  The  data  from  work  prior 
to  1911,  although  unreliable  in  some  respects,  have  been  included 
either  for  the  sake  of  comparison  with  the  later  work,  or  be- 
cause they  represent  for  some  reactions  the  only  results  avail- 
able. Repetition  of  the  earlier  work  should  be  undertaken 
where  it  has  not  already  been  done. 

A  general  discussion  of  the  ^/n  values  will  be  found  in 
§§  48-50. 

2>  Wni.  Duane  and  O.  Scheuer,  Le  Radium  10,  33-46  (1913). 
"O.  Scheuer,  Conip.  rend.  159,  423-6   (1914). 
"  Wm.  Dunne  and  A.  Lnbordo,  Lc  Uadliim  7,  162-4   (1910). 
"E.  E.  Wourtzel,  ibid.  11,  289-98;  332-47  (1919). 


IONIZATION  AND  RADIOCHEMICAL  EFFECtS 


it 


TABLE  VII " 

/.    Gaseous  Systems 

Statistical  Comparison  of  Ionization  and  Chemical  Action  by  a  Particles 


N  =  Total  Pairs  of  Ions. 

Reaction  Data  of 

+  02=(2H20)    (Moist)     C.&R. 

(Dry) 
(130°  C.) 
(Dry  or  moist)        S.^^ 

II  <l  L  31 

W>2 


M  =  Total  Number  of  Molecules. 


Chem.  Action 
Designation 
ofM. 
M 


,S)  =  H^  +  (S) 

;o,  =  2C0  +  O2 

u 

I;    " 
ICl  =  H,  +  CI2 
,  +  3H2  =  2NH3 


■T 

H2  +  Br^  =  2HBr 

3O2  :=  2O3 

2C0  =  CO2  +  (C) 

N,0  =  N,  +  0 
or  =:  (N  +  NO) 

2H,0  =  2H,  +  0, 

JL  +  CI2  =  (2HC1) 
It 

■H,0)  =  2H,  +  0 

W.32 


M 

M 


H3O 

« 

U 
It 

tl 


CO2 

mall 

NH, 


M/N 

0.65  to  0.81 

0.52  to  0.93 
1.59 
3.7 
4.0 
2.65 

0.38 


%  Energy 
Utilized 

4.9 


34.5 
6.7 

2.6 


Very  small  quantity  of  decomposition. 
C.&R.2«         M 


W.32 

U.33 

W.32 

L.3* 

L.35 

C.  &  R.2« 

W.32 

C.  &  R.28 

D.  &  S.3« 
B.&T.^^ 

J.  &  R.3« 


M 


HCl 


M 


0.25 

0.40 
0.80  at   18° 
2.55  "  315° 

0.76 

0.25 


1.2 

1.8 
0.6 


(N,  +  H,) 
Very  little  ammonia  formed  (chem.  anal.) 


M 


JIBr 


M 


0. 


M 


M 


CO 
NO 


M 


0.54 

0.50 

1.86 
1.74  at    18° 
2.16  "  -78° 
2.32  "  220° 


0.5 

2.0 

3.9 
4.0 


H2O         Very  little  action. 


M 


(H,  +  CU 


//.    Liquid  Systems 
D.30  Mh^o 

C.  &  R.2« 

•JJ  40  tt 


4000. 
100-1000 


(0.16) 

0.36 
0.41 


(1.0) 


S6  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

TABLE  Yll— Continued 
Reaction 

2HBr  =  H2  +  Br2 

KI  (in  acid  soln.)  =  (I  +  K^) 

Ice  (2H2O)  =  2H2  +  O2 

(-I^J-)  rr:  Jv  -|-  i  L/.  ygiy  little  decomposition  observed  for  penetrating  rays 

(Pblg)  =  Pb  +  Ij 


Dafa  0/ 
D.  &  S.3« 

C/iem.  Action 

Designation 

ofM 

^H,0 

0.86  to  1.05 

%  Enersfy 
Utilized 

6.4 

L.»* 

^HBr 

2.6 

2.2 

f< 

Mki 

0.76 

///.    Solid  Systems 

D.&S.«« 

Mh,0 

0.05 

0.3 

(PbCl^)  =  Pb  +  CI2  "  "     «  "  «      u        „       „ 

(it  Dorgj  ^=:  xD  -j-  ijT2  No  decomposition  observed  for  penetrating  rays. 

» Table  VII  Is  corrected  and  extended  from  table  of  Lind,  Joum.  Phys.   Ghent.  16,  p.  589  (1912) 

"A.  T.  Cameron  and  Wm.  Ramsay,  Joum.   Chem.  80c.  Lond.  93,  965  (1908).     See  §§29  and  30. 

»0.  Scheuer,  Comp.  rend.,  159,  423  (1914).    See    §  38. 

»»Wm.  Duane  and  A.  Laborde,  Le  Radium  7,    162  (1910).    See  §  29. 

"S.  C.  Llnd,  Journ.  Amer.  Chem.  Soc.  41,  531  1919).     See  §§  42,  44. 

»»E.  E.  Wourtzel,  Le  Radium  11,  289;  332  (1919).     See  §  39. 

"F.  L.  Usher,  Joum.  Chem.  80c.  Lond.  97i    389  (1910).     See  §  31. 

«*S.  C.  Llnd,  Le  Radium  8,  289  (1911). 

"S.  C.  Llnd,  Sitzh.  Akad.  Wisa.  Wien  Ila,  120,  1709  (1911)  ;  Amer.  Chem.Joum.,  47,  397  (1912). 
See  also  %  33. 

"Wm.  Duane  and  O.  Scheuer,  Le  Radium  10,   33  (1913).     See  §  37. 

"  (M.  Bodenstein)  and  H.  S.  Taylor,  Journ.  Amer.  Chem.  Soc.  37,  24  (1915)  ;  38,  280  (1910).  Id 
»  Bodenstein,  Zeit,  EleJctrochem.22,  53-61   (1916).     See  also  §  55. 

"Jorlssen  and  Ringer,   Ber.   39,   2093    (1906).     Compare  Lind,   J.   Phys.  Chem.  16,  610. 

"A.  Debierne,  Comp.  rend.  148,  703  (1909). 

*»F.  L.  Usher,  Jahrh.  d.  Radioakt.  u.  Elektr.  8,  323  (1911).     See  §  47. 

«S.  C.  Lind.  Joum.  Phys.  Chem.  16,  608  (1912). 


IONIZATION  AND  RADIOCHEMICAL  EFFECTS  87 

37.  Reactions  in  Liquid  Systems — Results  of  Duane  and 
Scheuer  on  the  Decomposition  of  Water,  Ice  and 
Water  Vapor. 

As  may  be  seen  from  Table  VII,  the  M/N  ratio  appears  to 
be  of  the  same  order  in  the  few  liquid  reactions  that  have  been 
investigated  as  in  the  majority  of  gas  reactions.  From  the  chemi- 
cal point  of  view  this  may  be  regarded  as  a  matter  of  some  sur- 
prise, but  so  far  as  the  ionization  is  concerned,  it  has  been  found 
that  variation  of  pressure  of  a  gas  results  only  in  shortening  the 
range  of  the  a  particle  without  affecting  the  total  ionization 
produced.  There  is  no  apparent  reason  why  this  should  not 
continue  to  be  true  on  passing  to  very  high  pressures  and  over 
into  the  liquid  state.  The  general  assumption  has  therefore 
been  made  in  the  calculations  involved  in  Table  VII  that  the 
total  ionization  by  the  complete  absorption  of  a  radiation  is  the 
same  as  would  be  produced  if  the  total  absorption  of  the  a  par- 
ticle occurred  in  the  same  substance  in  the  gaseous  state.  Owing 
to  the  lack  of  suitable  experimental  methods  of  determining  the 
ionization  produced  in  liquids  by  radiation,  it  has  not  been  pos- 
sible to  put  this  conclusion  to  the  test,  but  if  the  generality  of 
the  equivalence  between  chemical  effects  and  ionization  be  con- 
ceded, then  the  evidence  of  Table  VII  for  liquids  constitutes  a 
confirmation  of  the  ionization  relations  assumed,  at  least  within 
very  approximate  limits. 

The  work  of  Duane  and  Scheuer  (loc.  cit.)  carried  out  in  the 
laboratory  of  Mme.  Curie  on  the  decomposition  of  water  in  its 
three  states  of  aggregation  is  one  of  the  most  careful  and  com- 
plete researches  in  the  field  of  radiochemistry.  The  experi- 
mental method  for  the  liquid  and  solid  states  consisted  in  col- 
lecting purified  emanation  in  a  thin  capillary  glass  tube  (§33) 
in  which  it  was  allowed  to  act  upon  a  layer  of  water  or  ice 
sufiicient  to  absorb  the  <x  radiation  completely.  The  quantity 
of  hydrogen  and  oxygen  liberated  was  measured  in  a  eudiometer 
tube  and  the  excess  of  hydrogen  was  determined  after  sparking 
the  mixture.  By  comparing  the  rate  of  reaction  with  the  decay 
curve  for  emanation  it  was  found  that  the  two  coincide  perfectly 
if  the  volume  of  gas  liberated  is  corrected  for  the  oxygen  retained 
as  H2O2,  which  was  measured  chemically  and  found  to  corre- 
spond to  the  excess  of  hydrogen.    The  conclusion  was  drawn  that 


88  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

water  is  decomposed  in  a  primary  reaction  and  that  H2O2  is 
formed  by  the  secondary  action  of  nascent  oxygen  on  water.  A 
very  interesting  confirmation  of  this  view  was  obtained  in  the 
examination  of  the  gases  liberated  by  the  action  of  a  rays  on  ice 
at  —183°  C,  which  were  found  to  consist  wholly  of  electrolytic 
gas,  indicating  that  ice  at  this  temperature  is  not  acted  on  by 
nascent  oxygen  to  form  HgOg. 

The  comparison  of  the  electrical  and  chemical  effects  was 
made  by  allowing  the  emanation  to  decay  to  a  value  where  the 
saturation  current  method  could  be  applied  directly.  The  origi- 
nal quantity  of  emanation  was  calculated  from  the  decay  law. 
The  number  of  gas  molecules  formed  from  water  is  1.06  times 
the  total  number  of  pairs  of  ions  that  would  be  formed  in  air 
in  the  total  absorption  of  the  a  radiation.  Or  expressed  a  little 
differently,  the  a  rays  capable  of  producing  an  ionization  cur- 
rent of  one  ampere  in  air  will  decompose  water  giving  0.1594 
cm.^Hg  and  0.0797  cm.^Og,  values  of  the  same  order  as  0.125 
cm.^Hg  and  0.0615  cm.^Oa  which  would  be  liberated  per  ampere- 
second  in  electrolysis.  In  Table  VII  the  M/N  value  calculated 
from  the  results  of  Duane  and  Scheuer  is  for  ionization  in  HgO 
instead  of  in  air,  taking  the  value  for  the  total  specific  ioniza- 
tion of  H2O  as  0.82  that  of  air. 

The  action  of  a  rays  on  ice  and  on  water  vapor  is  much  less 
efficient  than  on  liquid  water,  not  more  than  5%  as  much  re- 
action being  found  in  maxima.  In  the  case  of  water  vapor  the 
emanation  was  mixed  directly  with  the  vapor  at  three  atmos- 
pheres pressure  at  170°  C;  the  excess  of  hydrogen  amounted 
to  about  50%.  Duane  and  Scheuer  express  the  opinion  that  the 
low  efficiency  of  the  action  of  a  rays  on  water  vapor  is  due  to 
recombination  of  the  products. 

In  Table  VIII  will  be  found  the  results  of  Expt.  Ill  from 
Duane  and  Scheuer  {loc.  cit.).  Two  additional  columns  have 
been  added  to  show  the  course  of  the  reaction  compared  with 
the  decay  of  emanation.  It  will  be  noticed  that  the  reaction 
runs  slightly  behind  the  decay  of  emanation,  but  if  correction 
be  made  for  the  deficiency  of  oxygen  according  to  the  excess 
of  hydrogen,  the  agreement  is  within  a  few  tenths  per  cent  in 
nearly  all  cases.  The  most  probable  value  for  the  decompo- 
sition of  water  by  emanation  is  390  cm.^  of  electrolytic  gas  per 
curie. 


IONIZATION  AND  RADIOCHEMICAL  EFFECTS 

TABLE  VIII 


89 


Decomposition  of  Water  by  Emanation  according  to  Duane  and 

Scheuer 

Initial  Emanation  191.5  milli-curies. 


Days, 

Hrs. 

0 

16 

1 

16 

3 

16 

4 

16 

5 

16 

6 

16 

7 

16 

8 

16 

10 

16 

17 

16 

22 

20 

32 

16 

48 

20 

Hz  +  Ooinc.c. 


0.1730 
0.4061 
0.7903 
0.9314 
1.0574 
1.1501 
1.2372 
1.3149 
1.4385 
1.6224 
1.6690 
1.7071 
1.7099 


%  Excess  Hr 
by  Vol 


16.1 
8.55 


6.90 


4.96 

2.77 
1.74 
0.48 


fo  Reaction 
Completed 


10.1 
23.9 
46.2 
54.4 
61.8 
67.2 
72.3 
76.9 
84.0 
94.9 
97.5 
99.7 
100.0 


% 

Emanation 

Decayed 


11.3 
25.9 
48.4 
56.8 
63.9 
69.9 
74.8 
79.0 
85.3 
95.8 
97.9 
99.7 
100.0 


It  may  be  pointed  out  that  the.  use  of  thin- walled  a  ray 
bulbs  excludes  the  participation  of  recoil  atoms  in  the  reaction, 
since  they  do  not  penetrate  the  wall.     (See  §  64.) 

Duane  and  Scheuer  saw  in  the  equivalence  between  the  ioni- 
zation produced  by  a  particles  and  the  decomposition  of  water 
"a  coincidence  having  a  profound  significance  in  the  theory  of 
electrolysis  and  the  decomposition  of  matter  by  the  a  rays  of 
radium." 

38.    Experiments  of  Scheuer  on  the  Formation  of  Water  by  a 
Radiation. 

The  very  careful  work  in  the  Curie  Laboratory  on  the 
chemical  effects  of  radium  radiation  was  extended  by  Scheuer  *^ 
to  the  formation  of  water  from  its  elements.  In  order  to  utilize 
the  a  rays  as  fully  as  possible  Scheuer  employed  rather  large 
glass  spheres  in  which  emanation  was  mixed  with  electrolytic 


*2  0.  Scheuer,  Comp.  rend.  159,  423-6  (1914). 


90  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

mixture  of  hydrogen  and  oxygen  under  increased  pressure.  After 
the  lapse  of  several  days  to  a  month  the  quantity  of  reaction 
was  determined  by  analyzing  the  gases.  In  all  cases  Scheuer 
reported  the  formation  of  some  HgOg,  which  in  one  case  repre- 
sented 16%  of  the  combined  hydrogen.  Two  experiments  were 
made  using  a  ray  bulbs  at  the  center  of  the  gaseous  mixture. 
The  ionization  was  calculated  by  means  of  the  Duane  and  La- 
borde  formula  (see  §  29),  but  since  this  is  directly  applicable 
only  to  air,  some  correction  for  specific  ionization  of  electrolytic 
gas  must  have  been  made.  The  M/N  values  for  four  different 
experiments  are  very  concordant  between  5.40  and  5.61  with 
an  average  of  5.51,  where  M  refers  to  the  total  number  of 
2H2  +  O2  molecules  combining,  which  is  equivalent  to  3.7  mole- 
cules of  water  formed  (disregarding  H2O2  and  treating  the  entire 
reaction  as  water  formation).  This  value,  though  much  higher 
than  the  older  ones  of  Cameron  and  Ramsay  (see  Table  VII), 
agrees  fairly  well  with  the  more-  recent  one  of  Lind  (loc.  cit.) 
3.9  (or  4.0  using  Lunn's  value  of  average  path  and  Hess  and 
Lawson's  value  for  number  of  a  particles  and  making  a  slightly 
different  assumption  as  to  the  position  of  Ra  A  in  the  reaction 
bulb). 

In  the  two  experiments  where  Scheuer  used  a  ray  bulbs  at 
the  center  of  his  mixture  he  still  employed  the  formula  of  Duane 
and  Laborde  to  calculate  ionization,  although  it  is  inapplicable, 
as  he  realized.  By  confining  all  the  emanation  at  a  point  source 
in  the  center,  the  full  radius  of  the  sphere  is  utilized,  instead  of 
the  average  path,  which  is  equal  0.5833  x  radius  (see  §  35) .    By 

multiplying  Scheuer's  values  for  ^^^''  +  ^^^    ■  (8.08  and  8.88)  by 

this  value,  one  obtains  4.7  and  5.1  in  fair  agreement  with  his 
other  values  reported  above.  Scheuer  also  carried  out  one  ex- 
periment with  oxygen  mixed  with  emanation  but  found  very  little 
ozone  under  his  experimental  conditions.  For  further  considera- 
tion of  Scheuer's  results  in  another  connection  see  §  43. 

Scheuer*^  also  investigated  the  reduction  of  CO  by  H2  in 
the  presence  of  radium  emanation,  which  reaction  had  already 
h'een  studied  under  somewhat  different  conditions  by  Stoklasa, 
Sebor  and  Zdobnicky,^*  who  found  formaldehyde  to  be  one  of 

*>0.  Scheuer,  Comp.  rend.  158,  1887-9  (1914). 

«*  J.  Stoklasa,  J.  Sebor  and  V.  Zdobnicky,  ibid.,  15G,  G4G-8   (1913). 


IONIZATION  AND  RADIOCHEMICAL  EFFECTS  91 

the  products  of  reaction.    This  was  confirmed  by  Scheuer,  who 
reported,  however,  that  the  final  product  is  mainly  CH^. 

Equilibrium  between  Hydrogen  and  Oxygen  mixed  with 
Emanation.  Although  this  subject  was  not  treated  by  Scheuer, 
it  is  very  appropriate  to  consider  it  in  connection  with  his  re- 
sults ori  the  formation  of  water  and  those  of  Duane  and  Scheuer 
(loc.  cit.)  on  its  decomposition.  Since  Duane  and  Scheuer 
showed  that  the  decomposition  of  water  vapor  is  very  slight,  we 
should  expect  that  the  homogeneous  gaseous  equilibrium  would 
lie  quite  far  on  the  side  of  combination.  No  direct  experiments 
have  been  made  on  the  subject.  In  the  case  of  the  heterogeneous 
equilibrium  between  hydrogen  and  oxygen  and  such  small  quan- 
tities of  water  as  could  result  from  the  combination  of  electro- 
lytic gas  in  small  volume  at  pressures  not  excessive,  the  solu- 
bility of  emanation  in  the  water  phase  may  be  neglected,  and 
we  should  expect  equilibrium  near  68%  of  combination  (on  the 
basis  of  M/N  for  formation  =  4,  and  for  decomposition  M/N  = 
1),  provided  that  the  condensed  water  is  so  distributed  that  it  is 
exposed  to  the  total  radiation  (equal  distribution  over  the  entire 
surface),  and  taking  the  average  path  as  0.58 x radius.  It  has 
been  shown  by  Lind,*^  however,  that  the  combination  proceeds 
under  the  experimental  conditions  just  mentioned  to  within 
nearly  1%  of  complete  combination.  This  was  attributed  to 
local  condensation  of  the  water  so  that  it  receives  only  a  small 
part  of  the  radiation  it  would  receive  if  evenly  condensed  over 
the  entire  surface.  The  heterogeneous  equilibrium  in  the  pres- 
ence of  larger  quantities  of  water  would  depend  upon  a  great 
number  of  factors  which  make  it  difficult  to  calculate.  The  case 
has  not  been  experimentally  investigated.  The  case  of  the  gen- 
eration of  high  pressure  in  a  sealed  radium  salt  (§  21),  owing  to 
the  decomposition  of  residual  water  of  crystallization,  is  interest- 
ing, because  theoretically  the  equilibrium  requires  low  instead  of 
high  pressure.  It  has  been  suggested  by  Lind  {loc.  cit.)  that 
the  gas  is  hydrogen  alone,  and  that  all  the  oxygen  combines  with 
the  radium  (or  barium)  salt. 

"S.  C.  Lind,  Trans,  Amer.  Electrochem.  Soc,  34,  214   (1918). 


92  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

39.    Experiments  of  Wourtzel  on  the  Decomposition  of  Gases. 

The  radiochemical  researches  of  the  Curie  Laboratory  were 
continued  by  Wourtzel  *®  whose  experimental  method  consisted 
in  mixing  purified  emanation  with  the  gas  to  be  decomposed  in 
spherical  glass  balloons  of  about  4  cm.  diameter,  enclosed  over 
mercury  but  separated  from  it  by  a  long  capillary  connection.  The 
quantity  of  emanation  employed  was  measured  by  the  y  ray 
method.  The  ionization  was  calculated  for  complete  absorption 
by  an  empirical  formula  K  =  Koo  (1  —  C/Rp) ,  in  which  K  is  the 
quantity  of  reaction  produced  by  1  curie  of  emanation  at  any 
pressure  p,  Koo  is  the  amount  of  reaction  at  infinite  pressure 
where  the  ionization  and  chemical  action  reach  a  maximum  owing 
to  complete  absorption  of  the  a  radiation,  R  the  radius  and  C 
a  constant.  The  specific  ionization  for  each  gas  was  calculated 
from  the  results  of  Bragg,*^  Kleeman  ^^  and  Taylor.'*^  The  amount 
of  chemical  action  was  determined  by  freezing  the  undecomposed 
gas  and  emanation  in  liquid  air  and  measuring  the  decomposition 
products  manometrically,  and  in  some  cases  also  chemically. 

The  decomposition  of  HgS,  NH3,  NgO,  and  CO2  was  studied. 
The  results  are  summarized  in  Table  IX. 

The  effect  of  temperature  on  the  reactions  observed  by 
Wourtzel  is  of  great  interest.  The  negative  coefficient  for  HgS, 
the  positive  one  for  NH.^,  the  minimum  for  NgO  at  18°  have  as 
yet  remained  unexplained.  With  respect  to  the  M/N  values  re- 
ported by  Wourtzel  at  temperatures  other  than  ordinary,  N  re- 
fers to  ionization  at  ordinary  temperature,  since  no  data  were 
available  at  other  temperatures.  The  failure  of  a  rays  to  de- 
compose CO2  is  further  considered  in  §  50. 

More  recently  Wourtzel  ^^  has  elaborated  a  theory  of  chemi- 
cal action  by  collision  with  the  a  particle,  as  distinguished  from 
the  ionization  theory  (see  §§  48-50).  He  employs  his  data  on 
the  decomposition  of  HgS,  NH3,  NgO,  and  those  of  Scheuer  (loc. 
cit.)  for  the  combination  of  electrolytic  gas  to  compare  with  the 
calculated  number  of  encounters  per  second  per  curie  of  emana- 

"E.  E.  Wourtzel,  Le  Radium,  11,  289-298;   332-347    (1919).     Journ.   Ruas. 
Phya.  Chem.  Soc.  Proc.  47,  210,  493  f)  (1915).     Comp.  rend.  157,  929  (1913). 
«W.  II.  Bragg,  Phil.  Mag.   (6)   13,  333  (1907). 
"R.  D.  Kleeman,  Proc.  Roy.  Soc,  79,  220   (1907). 
"T.  S.  Taylor,  Phil.  Mag.  (6)  21,  571   (1911). 
•®E.  Wourtzel,  Journ.  de  Phys.  et  le  Radium  (G)   1,  77-9G  (1920 ». 


IONIZATION  AND  RADIOCHEMICAL  EFFECTS 


93 


TABLE  IX 

Decomposition  of  Gases  by  Emanation  at  Different  Tempera- 
tures According  to  Wourtzel 


Gas 

Temp. 

Decomposedby 

1  Curie  Em. 

c.  c. 

M/N 

%  Energy 
Utilized 

H,S 

18° 

1011 

2.65 

6.7 

95° 

902 

2.17 

... 

220° 

707 

1.85 

... 

—  190° 

Solid  HgS :  Decomposition  of  same  order 

as  gas  at  18°. 

NH3 

18° 

282 

0.80 

1.2 

108° 

556 

1.58 

220° 

824 

2.33 

... 

315° 

900 

2.55 

... 

N,0 

—  78° 

823 

2.16 

18° 

737 

1.74 

(4.6) 

220° 

884 

2.32 

... 

CO2 

18° 

Very  little  decoi 

mposition  observed. 

tion.  The  agreement  with  the  measurements  of  chemical  action 
is  satisfactory,  especially  at  higher  temperatures.  Wourtzel 
suggests  that  at  the  lower  temperatures,  where  the  number  of 
encounters  exceeds  the  number  of  molecules  reacting,  some  .of 
the  encounters  are  not  effective.  In  the  case  of  N2O,  where  at 
all  temperatures  the  quantity  of  chemical  action  exceeds  the 
number  of  encounters,  Wourtzel  assumes  secondary  action.  This 
is  the  same  assumption  as  proposed  to  explain  excessive  reaction 
by  ionization,  and  it  hardly  appears  possible  with  present  data 
to  decide  between  the  two  theories  on  statistical  grounds.  It 
also  appears  questionable  if  Wourtzel's  assumption  in  calculat- 
ing the  number  of  encounters  made  by  a  particles  that  the  di- 
mensions of  the  particle  are  identical  with  those  of  the  helium 
atom  can  be  justified. 


Chapter  8. 

Kinetics  of  the  Chemical  Reactions  Produced  by 
Radium  Emanation. 

40.    Classification  of  the  Reactions. 

In  dealing  with  the  kinetics  of  chemical  reactions  produced 
by  radium  emanation,  two  general  factors  must  be  considered: 
(1)  change  in  the  agent  producing  the  reaction,  namely,  the  ra- 
dium emanation;  (2)  change  in  the  system  being  acted  on.  The 
decay  of  emanation  has  been  generally  recognized  as  one  of  the 
controlling  factors  of  the  rate  of  reaction  and  has  been  taken 
into  account  by  all  authorities  since  Cameron  and  Ramsay  first 
called  attention  to  it.  Besides  the  decay  of  emanation  another 
factor  controlling  its  effectiveness  in  producing  chemical  reaction 
is  its  distribution  in  the  system  being  acted  on.  In  a  gaseous 
system,  emanation  is  distributed  as  a  gas  and  its  effectiveness  is 
limited  only  by  the  effective  paths  of  the  a  particles  in  the  gas 
phase,  which  subject  has  been  treated  in  §  35.  In  a  liquid  sys- 
tem complete  absorption  of  the  a  radiation  occurs,  provided  the 
emanation  is  entirely  confined  within  the  liquid.  If  a  gas  phase 
exists,  the  distribution  of  the  emanation  between  the  two  phases 
must  be  known  as  well  as  all  the  other  factors  involved  in  de- 
termining the  proportion  of  radiation  from  the  gas  phase  that 
will  be  effective  on  the  liquid.  In  general,  the  reaction  in  the  gas 
phase  itself  will  be  negligible  compared  with  that  in  the  liquid. 
In  a  liquid  system  the  conditions  of  absorption  of  the  radiation 
remain  unchanged  at  maximum,  unless  a  gas  phase  should  be 
produced  by  the  reaction.  The  inconveniences  attending  such  a 
possibility  can  be  avoided  by  the  use  of  the  a  ray  capillary 
as  was  done  by  Duane  and  Scheuer  (§  37). 

In  gaseous  reactions  a  number  .of  cases  are  to  be  considered. 
The  simplest  case  is  that  of  an  elementary  gas  acted  on  in  such 
a  way  that  its  volume  and  concentration  remain  constant  while 
the  product  of  reaction  is  continually  removed  from  the  field  of 

94 


KINETICS  OF  THE  CHEMICAL  REACTIONS  95 

action.  If  its  concentration  (pressure)  diminishes  or  increases 
at  constant  volume,  then  this  change  must  be  taken  account 
of  in  regard  to  its  influence  upon  the  effectiveness  of  a  ray  absorp- 
tion. Such  a  case  would  be  represented  by  the  ozonization  of 
oxygen  mixed  with  emanation  at  constant  volume,  where  the 
ozone  formed  was  being  continuously  absorbed  by  mercury.  In  a 
mixture  of  gases,  a  simple  case  is  presented  by  electrolytic  hydro- 
gen and  oxygen;  the  product  water  is  condensed  and  nothing 
changes  in  the  gas  phase  except  the  pressure.  More  -complicated 
cases  arise  when  the  products  of  reaction  remain  in  the  gas  phase, 
as  in  NH3  decomposition.  Not  only  does  the  question  of  reverse 
reaction  then  present  itself,  but  also  that  of  an  indirect  effect 
of  the  products  in  rendering  the  radiation  effective  for  the  pri- 
mary reaction.  Furthermore,  in  the  case  of  mixtures  one  may 
inquire  whether  only  one  component  is  activated  or  more,  and 
what  the  effect  of  a  foreign  gas  will  be  in  the  mixture.  These 
and  other  similar  questions  are  natural  ones  from  the  kinetic 
standpoint..  But  before  they  can  be  attacked  it  is  necessary  to 
develop  a  general  kinetic  equation  for  the  influence  of  emanation 
on  gas  systems  as  a  function  of  the  pressure,  which  is  in  turn 
itself  a  function  of  the  rate  of  reaction,  dependent  upon  the 
quantity  of  emanation,  its  rate  of  decay,  the  size  of  the  vessel 
and  other  factors. 

41.  Development  of  General  Kinetic  Equation  for  the  Action 
of  Emanation  When  Mixed  with  Gases  in  Small  Vol- 
umes. 

The  following  equations  were  developed  by  Lind  ^  from  the 
standpoint  of  ionization,  but  the  final  general  form,  equation 
(3),  is  equally  valid  for  the  influence  of  emanation  without  any 
reference  to  ionization. 

If  N  be  the  number  of  pairs  of  ions  formed  in  a  time  in- 
terval t, 

dN/dt  =  3  X  3.72.10i«.Et.2.4.10^p.i.P/760.  (1) 

in  which  3  x  3.72.10^°  is  the  number  of  a  particles  emitted  per  sec- 
ond by  1  curie  of  emanation  in  equilibrium  with  Ra  A  and  C, 
Et  is  the  emanation  in  curies  at  any  time,  2.4.10*  is  the  number 
of  pairs  of  ions  formed  per  cm.  by  each  a  particle  along  the 

'S.  C.  Lind,  Journ.  Phya.  Chem.,  16,  571;  591-4   (1912). 


96  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

first  two  or  three  cms.  of  the  path  in  air  at  atmospheric  pres- 
sure, p  is  the  average  path  in  cms.  as  defined  in  §  35,  i  is  the 
specific  ionization  for  any  gas  compared  with  that  of  air  un- 
der the  same  conditions,  P/760  is  the  pressure  reduced  to  stand- 
ard conditions.  Equation  (1)  may  be  condensed  to  the  form: 
dN/dt  =  kEfP  =  kEoe-^^P,  in  which  k  is  the  ionization  constant 
including  all  the  constant  terms  of  (1). 

The  relation  between  chemical  action  and  ionization  may  be 
expressed  as: 

—  dC/dt  =:  const.  dN/dt, 

in  which  dC  is  the  change  in  concentration  of  the  substance 
undergoing  reaction. 

In  the  case  where  the  rate  of  chemical  action  is  measured 
manometrically  by  the  decrease  in  pressure, 

—  dP/dt=:ndN/dt,  (2) 

where  P  =  Po  —  jaN,  if  P  =  Po  for  N  =  0.  Combining  equations 
(1)  and  (2): 

~  l/[i.dP/dt  =  kEoe-^*  P,  and  dP/P  +  kfxEoe-^Mt  =  0 

log  P/Po  =  k^A.Eo(e-^*  —  1)  (3) 

P  =  P^e(»'AtA)Eo(e-^t  _  1)  ^^j 

Substituting  to  introduce  N: 

N=  (l/^l)Po  [1  — e^/^AEo(e-^t-l)  ]  (5) 

For  reactions  being  measured  manometrically  by  the  pressure 
change,  equation  (3)  can  be  conveniently  employed  as  a  kinetic 
equation  in  the  form: 

kn/X  =z  velocity  const.  =      ^  ^^    ° 

42.    Application  of  Kinetic  Equation  to  Experimental  Results. 

The  kinetic  equation  developed  in  §  41  will  be  strictly  appli- 
cable only  in  cases  where  all  the  constants  included  under  k  actu- 
ally remain  constant  during  the  course  of  the  experiment.  This 
will  be  true  for  the  specific  ionization  only  when  the  products 
of  reaction  are  removed  from  the  field  of  action.  As  already 
pointed  out  this  condition  is  satisfied  by  the  electrolytic  mixture 
of  hydrogen  and  oxygen  at  ordinary  temperature  through  the 


KINETICS  OF  THE  CHEMICAL  REACTIONS 


97 


condensation  of  water.  For  this  reason  the  kinetic  equation 
was  appHed  by  Lind  (loc.  cit.)  to  the  results  of  Cameron  and 
Ramsay  for  this  reaction,  as  shown  in  Table  X.  It  was  also  ap- 
plied to  some  of  the  other  reactions  studied  by  them  and  by 
Usher.  In  the  decomposition  of  CO  and  of  NHg  the  partial  pres- 
sures of  the  CO  and  NH3  are  used  instead  of  the  total  pressures, 
including  the  decomposition  products.  The  satisfactory  constant 
in  the  case  of  CO  indicates  the  correctness  of  such  a  procedure, 
and  the  absence  of  any  influence  of  the  CO2  formed  upon  the  rate 
of  reaction,  confirms  Wourtzel's  (§  39)  result  that  CO2  is  little 
acted  on  by  emanation.  On  the  other  hand  the  results  for  the  de- 
composition of  NH3  are  in  accord  with  the  equation  only  for  the 
first  part  of  the  reaction ;  during  the  latter  part,  where  the  prod- 
ucts have  accumulated,  the  apparent  rate  falls  off  owing  to  some 

TABLE  X 

Application  of  Equation  (3)  §  41  to  the  Results  of  Cameron  and 
Ramsay  and  of  Usher 


2H2  +  02 

=  (2H2O)  (moist). 

2C0 

=  C02+(C). 

Vol 

.  =  2.186  c. 

c. 

Vol.  (calcd.)  =z  2.567  c.  c. 

Eo  = 

=  0.0465  curie. 

Eo 

=:  0.025  curie. 

t  (days) 

P  (mm.) 

kyi/l 

t  (days) 

PofCO 

(mm.) 

kii/l 

0.0 

523.5 

0.0 

297.0 

1.02 

487.0 

(9.3) 

0.81 

282.0 

17.2 

2.07 

442.0 

(11.7) 

1.89 

263.0 

17.9 

3.07 

405.6 

12.9 

2.8 

251.0 

17.8 

4.13 

384.5 

12.7 

3.8 

245.0 

16.1 

4.99 

369.5 

12.8 

4.8 

233.0 

17.3 

6.11 

352.2 

12.8 

5.8 

225.0 

17.5 

7.07 

343.5 

12.6 

6.8 

221.6 

17.0 

9.11 

321.4 

13.0 

10.1 

218.0 

15.2 

10.16 

319.3 

12.7 

14.8 

206.2 

16.0 

11.04 

316.6 

12.5 

19.9 

208.4 

(14.9) 

12.10 

312.3 

12.5 

23.8 

201.4 

15.1 

97.0 

291.0 
Mean 

12.6 

26.8 

200.2 
Mean 

16.2 

..    12.71 

..    16.5 

THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 


TABLE  X— {Continued) 


2NH3  = 

N2  +  3H2  (Usher). 

N2  +  3H2  =  (2NH 

3  ? ), 

Vol 

.  =  2.406  c. 

c. 

Vol.  =  2.30  c.  ( 

■» 

Eo: 

=  0.145  curie. 

Eo  =  0.1195  curie. 

t  (days) 

i;(2)  (ccj 

k\i/\ 

t  (days) 

P  (total) 

k\i/l 

0.0 

0.909 

0.0 

745.6 

0.07 

0.895 

8.3 

0.79 

720.8 

(2.15) 

0.76 

0.781 

8.2 

1.76 

714.1 

(1.34) 

1.08 

0.735 

8.3 

2.77 

707.6 

(1.13) 

1.75 

0.664 

8.0 

3.77 

701.6 

1.04 

2.08 

0.630 

8.1 

4.85 

694.3 

1.03 

2.78 

0.581 

7.9 

5.77 

690.1 

1.01 

3.75 

0.527 

7.7 

6.76 

686.6 

0.98 

4.75 

0.493 

7.4 

7.76 

683.1 

0.98 

6.75 

0.441 

7.1 

9.76 

677.1 

0.97 

7.75 

0.431 

6.8 

11.0 

675.0 

0.97 

8.75 

0.421 

6.7 

12.8 

672.4 

0.96 

13.77 

0.399 

6.2 

14.8 

671.9 

0.98 

32.0 

0.385 

5.9 

17.9 

669.1 

0.94 

Mean  .... 



Mean 

.    0.99 

(-)  The  use  of  vol.  Instead  of  pr.  in  equation  (3)  is  readily  understood. 


kind  of  reverse  action,  such  as  seen  under  the  reaction:  No  +  3H2. 
Usher  found  little  or  no  NH3  formed,  but  the  manometric  effect 
would  be  in  the  same  direction  as  that  of  a  reverse  action,  even 
if  it  is  only  a  mechanical  loss  of  Hg. 

A  complete  kinetic  study  of  the  reaction  2H2  +  O2  was  more 
recently  undertaken  by  Lind  {loc.  cit.)  with  the  following  ob- 
jects: to  study  the  applicability  of  equation  (3)  over  wider  va- 
riations of  pressure,  to  enable  the  exact  evaluation  of  M/N,  to 
determine  the  influence  of  the  size  of  the  spherical  vessel,  and  to 
establish  the  effect  of  varying  the  proportions  of  hydrogen  and 
oxygen. 

The  apparatus  used  by  Lind  was  •a  simplified  form  of  that 
of  Cameron  and  Ramsay  and  is  shown  in  Fig.  6.  The  emanation 
was  measured  by  the  y  ray  method  after  introduction  into  the 
emanation  chamber.  By  comparison  of  the  columns  for  per 
cent  reaction  (completed)  and  per  cent  emanation  (decayed)  it 


KINETICS  OF  THE  CHEMICAL  REACTIONS 


99 


CO 

a 

^ 

o 

<i3 

00 

CO 

CO 

II  ^ 

.     '^ 

O 

^ 

B'^ 

o 

<i:> 
-< 

a 
^ 

C3     ^ 

CO          T-1 

i 

a  ° 
Z  il 

^ 

II 

?3w 

CI 

o 

+ 

11 

w 

o 

(M 

> 

5J 

»— 1 

X 

so 

CO 

•2 

w 

Q 

^ 

1 

H 

CO 

so 

^ 

=  1.925  cm. 

es. 

03 

ft^ 

^ 

B  3 

O 

03     O 

so 

^ 

=§• 

QS 

, 

tH 

so 

PN-^ 

« 

Q 

QO       o 

& 

KW 

t^ 

CO 

-^ 

II 

so 

> 

« 

O 

a. 

a. 

-^ 

Const, 

•t^cooiOT-Ht^cocoeoi:^ 
•cococdcocococdcococo 

CO 

P  t>;  -«iH  <M.  ^.  p  ^,  ^,  lO  (N  (N 

c5  (>i  i>^  t>^  rH  i>I  (m'  c5  05  o  o 

T-HrHC^COCO-^iOiOt^CT) 

g 

o 

s 

COCOt^QOcOt^OSCOCO 

OCOt^rHTthrH^i-HTtHOO 

ot^c^toddcococdt^d 

THCNCO-^iOiOCOl^QOO 

T-t 

a: 

r^oqt^osocoos^Tt^coco 
t-^QOcoo6r^i6t^dd<M'co 

^rHOt^OTjHCOT-IOOCOCO 

1 

COOOiOCX)lr^(Mt>iOO 
i-HtOiO(NOCOOii-i(NiO 

^o6rHQ6(HQ6i-3dc»o6(N 

i-H           ,-1           1-1           CM  tH  rH   (M 

00 

Si 

OOT-iT-iC^C^cOCOiOt>(N 

rH 

11 

;ODoqQqrHcop(Ncopio 

?5 

.1 

CDCOtJHtJHCOCOCOCOCOiO 
p  lO  (M,  p  rH(N  rH  00  »0  p  CO 
dcOcdcdi-HOTtHTHrHCOt^ 

i-i<MCOCO'^OCOI> 

i 

^1 

_CX)OOrJHiOcDiCiO'^CO 
Oi-iOC0C0'^CDC0O(NO 

Oi-iodcooTj^i^'^TtHdco 

T-lT-(Tt<iOCOCOI>.00O5O5 

poqooooc^c^ost^-cDT^ 
cdt>^o6QddiOi-iTHai(N'd 

TtH  CO  CO  (N  (M  !-<  ^  1-1 

1 

poqiqi>;COOCD(MiOOO 

dTjHQodi>c5i>^ddc>co 

1 

OOOiHiH(M(MCOTiHCOOO 

100  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

will  be  seen  that  the  former  runs  far  ahead  of  the.  latter,  espe- 
cially in  the  2  cm.  sphere  where  the  reduction  in  pressure  is 
greater.  This  shows  that  the  agreement  found  by  Cameron  and 
Ramsay  (§  30)  is  the  special  case  in  which  the  relative  pressure 
change  is  slight.  In  cases  of  large  variation  the  pressure  must 
be  taken  into  account  as  has  been  done  in  equation  (3).  Com- 
plete justification  of  the  treatment  is  seen  in  the  agreement  of 
the  k^i/X  values  over  the  whole  range  of  the  reaction. 


Fig.   6. 


43.    Influence  of  the  Size  of  the  Reaction  Vessel,  Law  of  the 
Inverse  Square  of  the  Diameter  of  the  Sphere. 

By  determining  the  velocity  constant  of  the  interaction  of 
electrolytic  hydrogen  and  oxygen  in  several  different  spherical 
vessels  of  diameters  from  1  to  5%  cms.,  Lind  (loc.  cit.)  estab- 
lished a  general  relation,  applicable  up  to  a  certain  size.  From 
the  standpoint  of  the  average  path  of  the  a  particles  in  limited 
spherical  volumes  (§  35),  the  nature  of  the  relation  can  be  pre- 
dicted. Increase  of  diameter  of  the  sphere  lengthens  the  average 
path  by  the  same  ratio  and  therefore  increases  the  quantity  of 
chemical  action  in  direct  proportion  to  the  increase  of  the  diam- 


KIKETICS  OF  THE  CHEMICAL  REACTIONS 


101 


eter.  The  pressure  effect,  however,  of  a  given  amount  of  chemi- 
cal action  will  be  inversely  proportional  to  the  volume  and, 
therefore,  to  the  cube  of  the  diameter.  Combination  of  these 
two  oppositely  directed  influences  predicts  that  the  pressure 
change  will  be  inversely  proportional  to  the  square  of  the  diam- 
eter of  the  spherical  reaction  vessel,  and  therefore  velocity  con- 
stants expressed  in  terms  of  pressure  (as  in  Equation  (3) )  will 
diminish  as  the  square  of  the  diameter  of  the  spherical  reaction 
vessel  increases.  By  comparing  the  velocity  constants  k\i/k  for 
the  2  cm,  and  5  cm.  spheres  in  Table  XI,  it  will  be  seen  that 
a  large  decrease  in  the  case  of  the  latter  was  observed.  In  the 
following  Table  XII  are  summarized  the  results  of  Lind  for 
spheres  of  several  different  diameters  obtained  by  the  same 
method. 

TABLE  XII 

Effect  on  the  Velocity  Constant  of  the  Reaction  2H2  +  02  = 
(2H2O)  of  Varying  the  Diameter  of  the  Reaction  Sphere 


Approx. 

Diam.  of 

Sphere  (cms.) 

True  Diam. 
D  (cms.) 

Vol.  of 

Sphere 

cm.^ 

(found) 

k\i/X  X  D^ 

1 
2 
3 

4 
5 

51/2 

0.9647 

1.925 

2.924 

3.963 

4.893 

5.613 

0.4701 
3.738 

13.272 

32.58 

61.32 

92.60 

(89.6)  « 
23.04 

9.92 

5.30 

3.52 

2.68 

Mean 

83.4 
85.3 

84.8 
83.2 
84.3 
84.1 

84.1 

'  Extrapolated  value.     See  Chapter  11  on  Recoil  Atoms. 


The  results  of  Table  XII  appear  to  establish  the  nature  of 
the  law  governing  the  influence  of  the  size  of  the  containing 
sphere  on  the  velocity  of  the  interaction  of  electrolytic  gas  as 
brought  about  by  radium  emanation  intermixed  with  it.  The 
fact  that  it  is  in  agreement  with  the  predictions  of  the  principle 
of  average  path  of  the  a  particles  supports  the  validity  of  the 
principle  and  its  application  in  calculating  ionization.  On  pass- 
ing to  volumes  other  than  spherical,  it  has  not  been  possible,  as 


'102  THE  CHEMICAL  EFEECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

stated  in  §  35,  to  give  a  mathematical  treatment  of  the  average 
path.  One  experiment  was  made  with  a  cylinder  1.8  cm.  in  di- 
,ameter  and  4  cms.  long  of  volume  6.787  c.  c,  equal  to  the  volume 
of  a  sphere  2.375  cms.  in  diameter.  Using  0.01219  curie  of 
jemanation,  a  value  of  k^i/X  was  obtained  of  14.8,  which  multi- 
plied by  (2.375)2  gives  83.1,  a  value  agreeing  within  the  limits 
of  experimental  error  with  those  of  the  spheres  in  Table  XII. 
Results  for  more  elongated  cylinders  are  to  be  desired.  The  use 
of  such  a  small  quantity  of  emanation  gave  a  pressure  reduction 
of  only  578.1  to  480.5  mm.  in  30  days.  Comparison  of  the  rate 
of  reaction  and  the  rate  of  decay  of  emanation  showed  agree- 
ment within  about  1%,  thus  confirming  the  experimental  realiza- 
tion of  Cameron  and  Ramsay's  special  case  (§  30). 

It  may  be  of  interest  to  inquire  how  great  the  diameter  of  the 
reaction  sphere  may  become  before  the  validity  of  the  relation 
k[x/X  =  84.1/D2  is  impaired.  Evidently  it  holds  for  the  largest 
bulbs  used  in  Table  XII  (5%  cms.  diam.).  By  applying  Equa- 
tion (3)  to  the  results  of  Scheuer  for  the  same  reaction  (§38)  a 
single,  value  of  kpi/X  may  be  found  for  still  larger  spheres.  In 
his  experiment  with  a  sphere  of  7.18  cms.  diameter  the  pressure 
diminished  from  1580  mm.  to  1433.8  mm.  in  26  days  with  0.0613 
curie  of  eijnanation,  which  gives  a  value  of  k\i/X  of  1.601.  The 
value  calculated  according  to  k[i/X  =z  84.1/D2  is  1.633,  showing 
that  for  ai  sphere  of  7  cms.  containing  2  atmospheres  of  elec- 
trolytic gais,  the  amount  of  reaction  found  is  only  2%  below  the 
theoretical  value  for  the  completely  utilized  average  path.  On 
going  up  to  Scheuer's  sphere  of  8.94  cms.  diameter  and  a  gas 
pressure  of  1680  mm.,  k[i/X  (exptl.)  is  only  0.987  against  1.054 
(theory).  And  in  a  sphere  of  6  cms.  diameter  at  the  high  pres- 
sure 11,445  mm.,  k\i/X  (exptl.)  is  only  0.3278  against  2.278  (the- 
ory). The  difference  is  due  to  the  number  of  a  particles  which 
can  not  complete  their  paths  at  this  pressure  before  being  com- 
pletely absorbed.  The  limit  of  the  applicability  of  the  formula 
for  average  path  appears  to  be  about  7  cms.  for  a  pressure  of 
1580  mm.  of  2H2  +  O^,  which  would  correspond  to  a  diameter  of 
10  cms.  at  1  atmosphere,  corresponding  to  an  average  path  in 
air  of  about  3.5  cms.  One  should  expect  that  the  general  law  of 
chemical  action  proportional  to  ionization  by  a  particles  would 
hold  only  over  the  first  two  or  three  cms.  of  path,  where  ioniza- 


KINETICS  OF  THE  CHEMICAL  REACTIONS  103 

tion  remains  constant.  This  would  doubtless  be  true  for  a  single 
type  of  a  particle,  for  example,  from  Ra  C  alone,  but  comparison 
with  Bragg's  ionization  curves  combined  for  all  the  a  particles  * 
shows  that  ionization  per  length  of  path  for  emanation  in  equilib- 
rium would  remain  almost  constant  up  to  about  4  cms.  from  the 
source  in  air. 

The  interaction  of  hydrogen  and  oxygen  mixed  with  radium 
emanation  can  come  to  an  end  through  the  approximate  ex- 
haustion either  of  the  emanation  or  of  the  gaseous  mixture  being 
acted  on ;  the  latter  takes  place  in  small  bulbs  with  high  emana- 
tion, the  former  in  large  bulbs.  The  actual  pressure  (P)  at  any 
time  t  (or  after  decay  of  all  emanation)  may  be  calculated  for 
any  given  case  from  the  equation: 

(log  P/Po)  /(Eo(e-^*— 1)  )  r=84.1/D2 

Contrary  to  the  opinion  expressed  by  some  authorities,  the 
ratio  of  quantity  of  emanation  to  quantity  of  reacting  gas  is  not 
important  from  the  kinetic  standpoint.  The  ratio  of  emanation 
to  reacting  gases  may  rise  continuously,  as  is  the  case  in  small 
volumes  where  the  gases  react  at  a  faster  percentage  rate  than 
the  emanation  decays,  may  pass  through  a  maximum  as  in  3  cm. 
spheres  with  about  100  millicuries  of  emanation,  or  may  fall 
continuously,  as  in  larger  spheres,  without  affecting  the  velocity 
constant.  This  shows  that,  while  the  ratio  of  emanation  to  gas 
influences  greatly  the  actual  velocity  of  reaction,  it  does  not 
change  the  value  of  k\i/l,  thus  proving  that  the  general  kinetic 
equation  proposed  holds,  regardless  of  the  relative  concentra- 
tions, except  as  provided  for  in  the  equation. 

It  may  also  be  mentioned  that  the  kinetic  equation  will  hold 
in  volumes  even  greater  than  those  at  which  the  average  path 
formula  no  longer  applies,  but  with  very  large  volumes  the  pres- 
sure changes  produced  by  attainable  quantities  of  emanation 
would  become  too  small  for  accurate  measurement.  There  is 
also  no  reason  to  suppose  that  the  same  formula:  velocity  con- 
stant =  const./D^  should  not  hold  for  other  reactions  than 
2H2  +  ^^2,  with  different  values,  however,  for  the  constants  in- 
volved. 

*W.  H.  Bragg,  "Studies  in  Radioactivity"  (1912),  p.  21;  Phil.  Mag.  (6) 
10,  323    (1905). 


104  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

44.    Use  of  Kinetic  Results  to  Evaluate  M/N. 

The  study  of  the  reaction  between  hydrogen  and  oxygen  pro- 
vides through  the  general  formula  for  spheres  (preceding  §) 
and  the  value  of  the  average  path  of  the  a  particle  in  spheres,  a 
method  of  evaluating  M/N  which  has  great  validity,  since  it  de- 
pends not  on  any  one  experiment  but  on  the  results  of  a  whole 
concordant  series  for  which  a  general  law  has  been  demonstrated. 
It  has  just  been  shown  that  k^i/X  =  84.1/D-.  Therefore  for  a 
sphere  with  D  =  1,  kfx/X  =  84,1,  and  it  is  only  necessary  to  evalu- 
ate k  and  solve  for  \i.  X  is  the  decay  constant  for  radium  emana- 
tion =  2.085  X  10"^  sec.~^.  \i  is  an  efficiency  factor  for  the  chemical 
effect  of  ions  and  may  be  expressed  as  ^  =  (M/N).(760/V.2.75x 
10^®) .  K  =  ionization  coefficient  =  number  of  a  particles  per 
second  for  1  curie  of  emanation  in  equilibrium  with  Ra  A  and  C 
(3  X  3.72  X  10^*^)  X  number  of  ions  per  a  particle  per  1  cm.  of 
path  (2.4  X 10*)  X  specific  ionization  of  the  gas  mixture  (for 
2H2  +  IO2)  1/3  (2x0.24  +  1.09)  =0.523)  x  average  path  for 
sphere  of  1  cm.  diam.  (0.2967  cm.)  x  1/760  (to  refer  to  1  mm. 
of  pressure) .    Therefore,  k  =  4.16  x  lO^M/760. 

Substituting  in  kfi/X  =  84.1  and  solving  for  M/N: 

M/N  =  6.0,  or  M^  ^/N  =  2/3  M/N  =  4.0.    (See  also  end 

of  this  §.) 
That  is,  for  each  pair  of  ions  produced  by  emanation  in  the 
gaseous  mixture  2H2  +  O2,  about  4  molecules  of  water  are 
formed.  This  is  calculated  on  the  basis  that  all  the  reduction  in 
pressure  represents  the  formation  of  water.  If  H2O2  is  formed 
it  must  have  but  temporary  existence,  since  in  one  experiment 
of  Lind  ^  an  intitial  pressure  of  982.9  mm.  of  electrolytic  gas  was 
reduced  in  12  days  by  0.1868  curie  of  emanation  at  a  volume  of 
3.375  c.  c.  to  only  11.5  mm.  The  M/N  value  4-0  is  in  fair 
agreetaent  with  that  of  Scheuer  3.7  (also  see  Kirkby,  p.  125) ,  but 
much  higher  than  the  older  values  of  Cameron  and  Ramsay  which 
were  less  than  1.0.  The  kinetic  evidence  of  §§  42  and  43  indi- 
cates that  Cameron  and  Ramsay's  low  results  are  to  be  attributed 
to  an  incorrect  report  of  the  quantities  of  emanation  used  in 
their  experiments,  which  were  not  the  result  of  direct  measure- 
ment in  loco  but  of  a  calculation  from  the  amount  of  radium  in 

»S.  C.  Lind,  Tranfi.  Amer.  Electrochcm.  Soc.  34,  214   (1918). 


KINETICS  OF  THE  CHEMICAL  REACTIONS  105 

the  original  solution.  If  the  evolution  or  collection  from  the 
solution  was  inefficient,  the  quantities  of  emanation  reaching  the 
reaction  chamber  may  well  have  been  several  fold  lower  than 
estimated.  For  example,  the  value  of  k\i/k  found  in  §  42  for 
one  of  Cameron  and  Ramsay's  experiments  was  12.71,  but,  from 
the  general  formula  for  a  vessel  of  that  volume,  should  have 
been  3243. 

In  calculating  the  M/N  value  for  the  formation  of  water  by 
the  average  path  method,  one  assumption  was  made  which  re- 
quires some  discussion.  The  average  path  was  calculated  as- 
suming that  all  a  particles  of  Ra  A  and  C  originate  on  the  wall 
of  the  containing  sphere,  which  involves  the  assumption  that 
Ra  A  after  being  generated  from  emanation  in  the  gas  phase  has 
time  to  diffuse  to  the  wall  before  emitting  its  a  radiation.  No 
data  having  a  very  direct  bearing  on  this  subject  appear  to  exist. 
A.  Debierne  ^  has  made  the  most  complete  examination  of  the 
rate  of  diffusion  of  active  deposit  by  using  parallel  plates  at 
different  distances  apart  exposed  to  emanation.  His  results 
show  that  the  practical  limits  of  diffusion  are  much  smaller  than 
the  theoretical  calculated  from  atomic  weights,  and  indicate  a 
particle  140  times  as  heavy  as  the  atom  of  the  decay  products. 
Some  direct  experiments  were  undertaken  by  Lind  {loc.  cit.)  by 
allowing  the  emanation  to  reach  equilibrium  in  electrolytic  gas 
in  glass  spheres  of  the  same  sizes  as  those  used  for  the  velocity 
of  combination.  By  suddenly  driving  the  gases  before  mercury 
into  a  new  vessel,  the  initial  y  radiation  in  the  latter  would  dis- 
close the  quantity  of  Ra  C  transferred  and  consequently  the  pro- 
portion left  on  the  wall  of  the  reaction  chamber.  In  a  sphere  of 
2  cm.  diameter  filled  with  electrolytic  gas  at  atmospheric  pres- 
sure the  percentage  of  Ra  C  transferred  was  6.7%;  or  93.3%  was 
deposited  on  the  original  wall.  From  a  6  cm.  sphere  11.6% 
passed  into  the  new  vessel;  or  88.4%  remained  on  the  wall  of  the 
original.  This  result,  not  to  be  expected  from  Debierne's  data, 
is  probably  due  to  heat  convection.  At  any  rate  it  is  evident 
that  under  the  experimental  conditions  a  large  part  of  the  Ra  C 
reaches  the  wall  of  even  a  6  cm.  sphere.  This  would  not  be 
necessarily  true  for  Ra  A  in  the  same  spheres  owing  to  its  much 
shorter  life,  but  the  velocity  constants  in  Table  XII  do  -not  in- 

8  A.  Debierne,  Le  Radium  G,  97-108   (1909). 


106  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 


i 


dicate  any  difference  between  large  and  small  spheres  for  effec- 
tiveness of  the  emanation  (plus  decay  products).  Whatever 
assumption  is  made,  therefore,  as  to  position  of  decay  products 
for  one  size  must  be  made  for  all.  The  one  made  was  that 
both  Ra  A  and  C  completely  diffuse  to  the  wall  before  decaying. 
If  one  assumes  instead  that  Ra  A  remains  largely  in  the  gas  phase 
while  Ra  C  diffuses  to  the  wall,  the  value  of  the  average  path  _ 

is  changed  from  0.5833  to  0.6667  times  the  radius,  and  the  M/N  ^ 

value  would  be  lowered  to  3.50.  From  considerations  to  be 
pointed  out  in  §  48  a  value  slightly  less  than  4  has  greater  prob- 
ability than  one  above  4.  This  discussion  is  deferred  to  §  48 
where  all  the  evidence  for  and  against  an  ionic  theory  of  the  a 
ray  effects  is  summarized. 


Chapter  9. 

Additional  Relationships  of  the  Eadiochemical 

Efeects. 

45.    Influence  of  Varying  the  Proportions  of  Hydrogen  and 
Oxygen. 

In  studying  the  interaction  of  hydrogen  and  oxygen  under 
the  influence  of  radium  emanation  mixed  with  the  gases,  the  ef- 
fect of  varying  the  relative  proportions  of  the  two  components 
was  investigated  by  Lind.^  The  effect  of  an  excess  of  either  gas 
on  the  rate  of  reaction  can  be  predicted  on  the  assumption  that 
the  change  in  rate  will  be  in  proportion  to  the  ability  of  the  mix- 
ture to  absorb  the  energy  of  the  a  particle,  which  is  in  proportion 
to  the  ionization.  The  specific  (molecular)  ionization  compared 
with  air  is  according  to  Bragg  (§  13)  1.09  for  oxygen  and  0.24 
for  hydrogen.  Consequently  an  initial  excess  of  oxygen  should 
increase  the  reaction  velocity  relative  to  that  of  the  normal  elec- 
trolytic mixture,  while  excess  of  hydrogen  should  produce  the 
opposite  effect.  The  velocity  constant  calculated  from  the  gen- 
eral kinetic  equation  should  be  initially  higher  than  the  normal 
value  in  the  case  of  excess  of  oxygen,  and  should  continue  to 
rise  as  the  mixture  becomes  relatively  richer  in  oxygen  with  the 
progress  of  the  reaction.  With  initial  excess  of  hydrogen  ex- 
actly the  opposite  should  be  true;  the  velocity  constant  should 
be  initially  abnormally  low  and  show  a  further  fall  as  the  mix- 
ture enriches  relatively  in  hydrogen. 

Both  cases  were  experimentally  investigated  and  the  predic- 
tions just  made  were  found  to  be  fully  confirmed,  as  will  be  seen 
from  Table  XIII.  Since  the  specific  ionization  now  becomes  va- 
riable, the  general  kinetic  equation  is  not  strictly  applicable. 
The  development  of  a  new  equation  taking  into  account  the 
changing  specific  ionization  or  "stopping  power"  is  so  compli- 
cated that  the  simpler  procedure  has  been  adopted  of  using  the 

^  S.  C.  Lind,  Journ.  Amcr.  Chein.  Soc.  41,  542  (1919). 

107 


108  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

equation  to  show  that  the  change  in  its  velocity  constant  is  pro- 
portional to  the  change  in  specific  ionization.  Since  the  velocity 
constant  (k^/X)  now  becomes  a  variable,  it  should  be  calculated 
over  short  intervals  to  avoid  undue  masking  of  its  variability. 
To  accomplish  this  the  value  of  k\i/X  is  calculated,  not  from  the 
beginning  through  the  entire  time  interval  in  each  case,  but 
from  each  measurement  to  the  next,  a  procedure  quite  commonly 
employed  in  chemical  kinetics.^ 

The  equation  may  be  written  in  this  form: 


m- 


^^  (6) 


Eo  (e-^^i  — e-^*2) 


Table  XIII  gives  the  data  for  the  initial  mixture  4H2  to 
IO2.  In  column  5  the  application  of  equation  (6)  shows  that 
(kfx/X)'  is  not  constant  but  falls  approximately  as  required  by 
the  change  in  specific  ionization  (compare  column  6) .  Column  6 
is  calculated  from  the  normal  value  (kji/X  =  84.1/D2)  _  iqq^ 
for  a  sphere  of  the  size  used,  and  from  the  change  in  specific 
ionization  calculated  by  applying  the  simple  law  of  mixtures  to 
the  values  for  pure  hydrogen  and  oxygen. 

A  consideration  of  the  results  shown  in  Table  XIII  will  throw 
light  upon  an  important  question,  namely,  whether  it  is  only  one 
component  of  the  reaction,  or  both,  which  are  activated  by  the 
a  radiation ;  or,  in  terms  of  ionization,  are  both  the  hydrogen  and 
oxygen  ions  capable  of  taking  part  in  the  chemical  reaction  pro- 
duced at  ordinary  temperature?  Since  the  rate  of  reaction 
appears  to  be  proportional  to  the  specific  ionization  of  the 
mixture,  this  question  is  already  answered  in  favor  of  the  suppo- 
sition that  both  ions  are"  active.  But  a  still  more  definite  answer 
is  obtained  by  calculating  (kfx/X)'  for  partial  pressures  of  the 
components.  In  the  last  column  of  Table  XIII  are  values  of 
(k[i/'k) '  calculated  from  the  partial  pressure  of  oxygen,  and  it  is 
seen  that  the  values  rise,  whereas  the  reaction  is  really  slowing 
up  from  the  rate  shown  by  a  normal  mixture,  which  must  be 
interpreted  as  meaning  that  the  partial  pressure  of  oxygen 
alone  does  not  control  the  rate  of  reaction.  The  calculation  from 
partial  pressures  of  hydrogen  would  in  this  case  not  differ  suf- 

« J.  W.  Mellor,  "Chemical  Statics  and  Dynamics"   (1904),  pp.  31,  3G,  37. 


THE  RADIOCHEMICAL  EFFECTS 


109 


TABLE  XIII 

Effect  of  the  Excess  of  H^  on  the  Velocity  Constant  of  the  Re- 
action  2H2  +  0,  =  (2H2O) 

Init.  Mixt.  4H,:10,.    Vol.  =  11.64  c.  c.    Diam.  =  2.812  cm. 
Eo  =  0.1169  curie. 


Days 

Hrs. 

0 

0.0 

0 

19.25 

1 

3.25 

1 

23.00 

2 

23.67 

4 

19.33 

6 

3.75 

7 

19.67 

8 

23.75 

11 

19.33 

13 

22.33 

15 

22.50 

Total  Pr. 

Partial 

(k[i/l/ 

(k\i/iy 

mm.  Hg. 

Pr.O, 

(found) 

(calcd.) 

682.8 

136.6 

605.9 

110.9 

7.92 

7.93 

580.3 

102.4 

7.30 

7.50 

528.2 

85.0 

7.17 

7.38 

480.6 

69.2 

6.80 

7.17 

425.2 

50.7 

6.42 

6.89 

397.9 

41.6 

6.24 

6.62 

375.8 

34.2 

5.74 

6.46 

363.9 

30.2 

5.89 

6.30 

346.7 

24.5 

5.24 

6.10 

338.4 

21.8 

5.50 

5.97 

332.9 

19.9 

5.65 

5.90 

(h\i/iy 

for  Par. 
Pr.O, 


13.20 
13.50 
14.20 
14.90 
16.30 
18.61 
19.50 
22.71 
22.75 
27.91 
30.24 


ficiently  from  that  by  the  total  pressures  to  make  a  decision,  but 
may  be  undertaken  for  mixtures  with  initial  excess  of  oxygen. 

In  Table  XIV  will  be  found  data  for  mixtures  with  excess  of 
oxygen. 

In  Table  XIV  the  comparison  with  the  theoretical  values 
calculated  from  ionization  is  not  made,  since  the  change  in  spe- 
cific ionization  is  not  so  great  as  in  the  case  with  the  mixture 
4H2:1  O2  (Table  XIII),  but  it  can  be  seen  that  the  constants 
show  a  tendency  to  rise  in  all  cases  and  begin  abnormally  high 
when  compared  with  the  normal  value  for  electrolytic  mixture, 
as  required  by  theory. 

From  the  data  for  the  2  to  1  and  4  to  1  mixtures  in  Table 
XIV  it  will  be  observed  that  when  the  hydrogen  is  exhausted, 
the  pressure  reduction  does  not  stop  entirely,  but  the  velocity  of 
reaction  falls  at  once  to  one  of  an  entirely  lower  order  as  indi- 
cated by  the  velocity  constants  in  the  last  column.  This  is 
caused  by  some  reaction  that  oxygen  alone  undergoes  when  acted 


110  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 


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THE  RADIOCHEMICAL  EFFECTS  111 

on  by  a  rays,  which  is  more  fully  discussed  in  the  following 
section. 

46.    Action  of  a  Rays  on  Pure  Oxygen  or  Pure  Hydrogen. 

The  limits  of  changing  the  proportions  of  hydrogen  and 
oxygen,  discussed  in  the  foregoing  section,  are  pure  oxygen  or 
pure  hydrogen.  According  to  the  results  of  Lind  (§  33),  under 
different  experimental  conditions,  ozone  is  formed  by  the  action 
of  a  rays  on  pure  oxygen.  In  the  presence  of  mercury  a  sec- 
ondary reaction  with  the  ozone  formed  might  be  expected,  which 
is  clearly  indicated  by  the  results  near  the  end  of  the  reactions 
in  Table  XIV.  Scheuer  [loc.  cit.)  found  that  emanation  mixed 
with  oxygen  led  to  very  little  pressure  reduction,  but  it  was  not 
stated  whether  the  reaction  took  place  in  the  presence  of  mer- 
cury. Direct  experiments  by  Lind  with  the  same  form  of  appa- 
ratus as  used  for  electrolytic  gases  (Fig.  6,  p.  100)  showed  that 
a  decided  diminution  in  pressure  does  take  place,  but  that  the 
velocity  of  reaction  is  dependent  upon  the  extent  of  the  surface 
of  mercury  that  is  exposed.  When  the  surface  is  only  that 
exposed  by  the  mercury  ordinarily  in  the  stem  of  the  reaction 
bulb,  the  reaction  is  relatively  slow;  but,  if  the  mercury  is 
allowed  to  rise  in  the  bulb  and  spread  out,  the  rate  of  reaction 
increases  many  fold.  This  probably  means  that  primary  ozoni- 
zation  takes  place  in  all  cases,  but  that  de-ozonization  also  takes 
place  unless  the  opportunity  for  ready  combination  with  mercury 
is  presented.  The  surface  of  the  mercury  becomes  black,  loses 
its  coherence,  clings  to  the  glass  and  is  finally  covered  with  a 
black  powder,  probably  mercurous  oxide.  The  repetition  of  this 
experiment  under  more  definite  conditions  offers  the  possibility 
of  an  independent  method  of  measuring  ozone  formation  by  a 
rays. 

In  the  case  of  pure  hydrogen  mixed  with  emanation  a  similar 
but  smaller  diminution  in  pressure  was  observed  by  Lind  [loc. 
cit.),  accompanied  by  a  darkening  of  the  mercury  and  a  loss  of 
its  coherence,  though  no  powder  became  visible  on  the  surface  as 
in  the  case  with  oxygen.  The  diminution  of  pressure  ceased  after 
a  time  and  could  not  be  made  to  proceed  further  by  increasing 
the  mercury  surface.  To  explain  reduction  of  pressure  in  hydro- 
gen exposed  to  a  radiation,  several  possibilities  present  them- 


112  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

selves.  Usher  ^  found  in  trying  f o  cause  hydrogen  and  nitrogen 
to  unite  under  the  action  of  emanation  that  the  reduction  in 
pressure  was  mainly  due  to  some  other  action  of  the  a  particles, 
presumably  a  purely  physical  one.  On  the  other  hand  Duane 
and  Wendt*  have  discovered  the  existence  of  an  active 
modification  of  hydrogen  produced  by  radium  emanation,  which 
reacts  chemically  with  sulfur  at  ordinary  temperature  to  form 
HgS  which  can  be  detected  by  passing  over  paper  impregnated 
with  a  solution  of  lead  acetate.  Langmuir  ^  has  reported 
the  discovery  of  a  very  active  atomic  form  of  hydrogen,  and 
recently  Wendt  and  Landauer  ^  have  described  the  activa- 
tion of  hydrogen  by  a  rays  and  by  the  corona  discharge,  and 
present  evidence  of  its  triatomic  nature.  Though  not  so  active 
as  monatomic  hydrogen,  the  triatomic  form  has  been  shown  by 
Wendt  and  Landauer  to  react  at  ordinary  temperature  with 
sulfur,  arsenic,  phosphorus,  mercury,  nitrogen,  and  both  neutral 
and  acid  KMn04.  It  is  unstable  and  reverts  to  the  ordinary 
form  in  about  one  minute.  It  can  be  distinguished  from  the 
monatomic  form  by  the  ease  with  which  it  passes  through  glass 
wool. 

47.    Comparison  of  the  Chemical  Effects  of  a  and  of  Pene- 
trating Rays. 

Since  the  chemical  reactions  produced  by  a  rays  have  been 
shown  to  be  at  least  approximately  proportional  to  the  ioniza- 
tion in  most  cases,  it  is  logical  to  inquire  whether  the  same  is 
true  for  the  chemical  effects  of  the  penetrating  rays.  At  any 
rate  the  question  should  be  carefully  investigated  experimentally. 
There  is  quite  a  divergence  of  opinion  on  the  subject.  Besides 
the  experimental  difficulties,  which  are  serious,  some  of  the  early 
attempts  to  explain  p  ray  effects  were  directed  toward  a  consid- 
eration of  the  primary  charge  carried  by  the  p  particles  them- 
selves, which  are  of  course  very  insignificant  in  comparison  with 
the  large  number  of  electrons  liberated  and  positive  ions  produced 
by  the  passage  of  (3  particles  through  matter. 

»F.  L.  Usher,  Joum.  Chem.  Soc.  Lond.,  97^,  389  (1910). 

*Wm.  Duane  and  G.  L.  Wendt,  Phya.  Rev.   (2)   10,  116-128   (1917). 

»I.  Langmuir,  Joum.  Amcr.  Chcm.  Soc.  34,  1310-25;  36,  1706  (1914)  ;  37, 
417    (1915). 

•G.  L.  Wendt  and  R.  S.  Landauer,  Joum.  Amer.  Chem.  Soc.  42,  930-46 
(1920). 


THE  RADIOCHEMICAL  EFFECTS  113 

The  chemical  effects  of  p  and  y  rays  are  so  minute  for  nearly 
all  gas  reactions  that  a  direct  comparison  of  ionization  and 
chemical  action  has  not  been  possible  in  a  strictly  quantitative 
sense.  Of  course,  by  increasing  the  absolute  quantity  of  the 
radioactive  source  this  difficulty  could  in  part  be  obviated, 
although  this  is  hardly  possible  for  y  radiation,  the  relative  ioni- 
zation produced  by  which  is  of  the  order  of  1/10000  of  that  of 
the  corresponding  a  radiation.  But  a  still  more  serious  difficulty 
is  encountered  in  the  low  absorption  coefficients  of  p,  and  par- 
ticularly of  Y  rays,  which  precludes  the  possibility  of  anything 
approaching  complete  utilization  of  the  radiation  in  a  gaseous 
system  of  reasonable  dimensions.  For  this  reason  the  investiga- 
tion of  the  chemical  effects  of  penetrating  rays  has  been  mainly 
confined  to  liquid  systems  (§  28),  and  then  under  such  conditions 
that  a  very  small  proportion  of  the  y  radiation  is  absorbed. 

The  most  careful  comparison  of  a  and  p-y  ray  effects  has 
been  made  by  Usher.^  Using  emanation  in  a  glass  capillary 
tube  of  0.17  mm.  thickness,  0.208  cm.^  of  electrolytic  gas  was 
produced  by  the  action  of  the  penetrating  radiation  from  0.067 
mm.^  of  emanation  in  one  month  while  the  combined  action  of 
the  a  and  penetrating  radiation  from  0.025  mm.^  of  emanation 
till  completely  disintegrated  gave  a  total  of  5.840  cm.^  of  electro- 
lytic gas  (including  B.^  from  some  H2O2  formation).  Reduced 
to  the  same  quantities  of  emanation,  the  joint  effect  of  the  rays 
is  seen  to  be  about  75  times  as  great  as  that  of  the  penetrating 
rays  alone,  or  the  effect  of  the  latter  is  about  1.3%  of  the  com- 
bined effect.  This  is  about  what  one  should  expect  from  the 
relative  ionizations  or  kinetic  energies.  This  appears  to  be 
strong  evidence  in  favor  of  the  same  relationship  between  ioni- 
zation and  chemical  action  as  that  which  has  been  shown  to 
exist  for  a  rays. 

It  should  be  mentioned,  however,  that  a  different  interpre- 
tation was  put  upon  his  results  by  Usher  from  that  just  proposed. 
By  taking  into  account  all  the  soft  p  rays  which  were  not  able 
to  penetrate  the  thin  glass  wall,  and  by  assuming  that  each  one 
of  them  would  have  had  the  same  power  of  decomposing  water 
as  those  had  which  did  penetrate  the  wall.  Usher  estimated  that, 
where  emanation  is  dissolved  directly  in  water,  and  hence  all 

^F.  L.  Usher,  Jahrl).  d.  RadioaU  u,  Elcktr.  8,  323-34   (191X). 


114  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

non-penetrating  rays  are  absorbed,  the  proportion  of  decomposi- 
tion by  the  a  rays  is  not  more  than  twice  that  produced  by  the  p 
rays.  Apparently  Usher  was  led  to  this  view  through  the  assump- 
tion of  chemical  effect  proportional  to  the  primary  charges  of 
the  p  particles  themselves,  according  to  which  all  p  particles 
would  produce  the  same  chemical  effect,  regardless  of  their 
velocity,  kinetic  energy,  or  penetrating  power.  This  is  not  only 
contrary  to  the  idea  of  equivalence  of  ionization  and  chemical 
action,  since  the  charge  carried  by  the  p  rays  would  fall  many 
thousand  fold  short  of  accounting  for  the  chemical  effects  in  a 
sense  consistent  with  Faraday's  Law;  but,  in  the  case  of  the  very 
soft  p  rays,  the  law  of  the  conservation  of  energy  would  be  con- 
traverted,  since  they  do  not  possess  enough  kinetic  energy  to 
account  for  the  amount  of  water  decomposition  assumed  by 
Usher.  In  other  words,  the  chemical  activity  of  a  or  ^  rays  must 
be  attributed  to  their  kinetic  energy  and  ionizing  power,  not  to 
their  own  charges,  which  in  comparison  with  the  secondary 
charges  produced  are  wholly  insignificant,  as  would  be  shown 
by  the  fact  that  a  single  a  particle  from  Ra  C,  having  two  posi- 
tive elemental  charges,  produces  in  its  total  path  in  air  about 
237,000  pairs  of  positive  and  negative  charges,  and  even  more 
than  this  in  some  other  gases.  The  total  ionization  for  water 
by  1  a  particle  has  not  been  directly  measured,  but  is  probably 
of  the  order  195,000  pairs  of  ions. 

In  §  36,  Table  VII,  the  results  of  Usher  for  the  decomposition 
of  water  by  emanation  are  seen  to  be  considerably  lower  than 
those  of  Duane  and  Scheuer,  using  the  a  ray  capillary  method. 
Debierne®  has  measured  the  decomposition  of  water  by  the 
penetrating  rays  from  a  radium  salt,  and  found  that  0.115  cm.^ 
of  electrolytic  gas  are  formed  per  day  per  gram  of  radium.  This 
rate  of  decomposition  is  somewhat  lower  than  that  found  by 
Usher  per  curie  of  emanation,  as  would  be  expected,  owing  to 
the  greater  absorption  of  radiation  in  Debierne's  apparatus  by 
the  double  glass  wall  and  by  the  salt  itself. 

48.     General  Discussion  of  Ionic-Chemical  Equivalence. 

All  the  experimental  evidence  bearing  on  this  subject  has  been 
presented  in  the  foregoing  sections  except  that  pertaining  to 

8 A.  Debierne,  Comp.  rend,  148,  703-5  (1909). 


THE  RADIOCHEMICAL  EFFECTS  115 

recoil  atoms  which  will  be  treated  in  Chapter  XI.  A  general 
summary  of  the  results  is  not  without  interest,  although  it  may 
be  impossible  to  reach  a  final  conclusion  acceptable  to  all  author- 
ities, from  the  data  at  present  available. 

It  has  been  shown  that  in  nearly  all  the  reactions  brought 
about  by  a  rays  that  have  been  investigated  there  is  an  approxi- 
mate statistical  agreement  between  the  number  of  ions  generated 
and  the  number  of  molecules  acted  on.  This  appears  to  be  true 
to  the  same  degree  of  approximation  both  in  gaseous  and  liquid 
systems.  The  results  have  been  brought  together  for  compari- 
son in  Table  VII,  §  36.  It  will  be  seen  that  the  M/N  ratio  varies 
in  different  reactions  from  about  0.5  to  about  4.0.  An  agreement 
within  these  limits  for  such  a  variety  of  reactions  proceeding 
both  with  and  opposed  to  the  chemical  free  energy  in  both  liquid 
and  gaseous  systems,  when  the  disagreement  might  have  been 
many  million  fold  in  either  direction,  appears  to  have  funda- 
mental significance  and  to  warrant  the  application  of  a  modified 
form  of  Faraday's  Law  to  these  reactions.^ 

Besides  the  direct  evidence  from  a  particles,  it  was  shown  in 
§  45  that  when  the  proportions  of  hydrogen  and  oxygen  are 
varied,  the  reaction  to  form  water  changes  its  rate  in  a  ratio 
that  can  be  predicted  from  the  change  in  specific  ionization  of 
the  mixture.  Passing  to  other  forms  of  radiant  energy  which 
produce  ionization  accompanied  by  chemical  action,  it  was  shown 
in  §  47  that  the  same  equivalence  holds  in  the  decomposition  of 
water  by  p  radiation.  In  §  33  the  results  of  Krueger  for  the 
ozonization  of  oxygen  by  Lenard  rays  (high  velocity  electrons) 
were  cited  to  show  that  the  same  relation  exists;  finally,  in 
Chapter  XI  it  will  be  shown  that  the  recoil  atoms  from  a  radi- 
ation cause  the  combination  of  Hg  and  O2  in  the  same  propor- 
tion to  the  ionization  as  found  for  a  particles.  Such  evidence 
has  been  sufficient  to  convince  many  authorities  that  ionization 
is  directly  involved  in  the  production  of  chemical  reaction.  Qn 
the  other  hand  the  results  of  Scheuer  on  the  formation  of  water 
(§  38)  and  those  of  Wourtzel  (§  39)  on  the  decomposition  of  HgS 
and  of  N2O,  which  show  M/N  values  exceeding  unity  by  two  to 
four  fold,  have  convinced  Debierne,  Scheuer,  and  Wourtzel  that 

»S.  C.  Lind,  Trans.  Amor.  Elcctrochem.  8oc.  21,  177-84  (1911);  Journ. 
Phys.  CJiem.,  16,  564-G13 ;  Le  Radium,  9,  426-31;  Zeit.  phys.  Chem.,  84, 
759-61    (1913). 


116  THE  CHEMICAL  EFFECTS   OF  ALPHA  PARTICLES  AND  ELECTRONS 

the  ions  are  not  the  intermediate  products  causing  the  chemi- 
cal action.  Debierne  ^°  has  proposed  a  theory  of  thermal  decom- 
position along  the  path  of  the  a  ray  but  extending  outside  the 
limits  of  ionization  and  therefore  statistically  exceeding  the  ioni- 
zation. Wourtzel  {loc.  cit.)  finds  in  the  negative  temperature 
coefficients,  which  he  obtained  for  the  decomposition  of  HgS 
and  of  NgO,  grounds  for  rejecting  the  thermal  theory  of  Debierne 
and  has  substituted  a  theory  of  collision. 

As  already  stated,  the  writer  is  of  the  opinion  that  the  statis- 
tical agreement  between  ionization  and  chemical  action,  although 
inexact,  points  strongly  to  the  intermediation  of  ions  in  bringing 
about  the  chemical  reactions.  The  departures  from  the  direct 
requirements  of  electrical  and  chemical  equivalence  are  not  too 
great  to  be  brought  into  accord  by  making  possible  assumptions 
in  regard  to  the  mechanisms  of  reaction,  which  assumptions  are 
quite  within  reason,  although  it  is  impossible  with  present  data 
either  to  prove  or  disprove  them  absolutely.  At  any  rate  the 
departures  of  M/N  from  unity  are  quite  small  when  compared 
with  the  real  exceptions  to  be  taken  up  in  the  following  section. 
It  might  also  be  mentioned  that  whether  ionization  is  primarily 
involved  in  the  chemical  reactions  brought  about  by  radiation, 
or  whether  it  is  a  secondary  accompaniment,  it  is  at  the  present 
time  the  most  convenient  index  of  reference  and  can  readily  be 
made  a  means  of  comparing  chemical  action  with  any  factors 
involved  in  the  absorption  of  the  energy  of  radiation. 

Before  going  on  to  a  consideration  of  the  large  exceptions 
from  the  general  rule  of  equivalence  of  ionization  to  chemical 
action,  the  case  of  the  combination  of  electrolytic  hydrogen  and 
oxygen  under  the  influence  of  a  rays  will  be  used  as  an  example 
to  illustrate  the  possibility  of  proposing  a  mechanism  of  reaction 
that  will  explain  the  value  Mjj  q/N  =  4,  without  violating  the 
general  principle  of  equivalence. 

Millikan,  Gottschalk  and  Kelly  (loc.  cit.)  have  shown  that 
the  ionization  of  a  number  of  ordinary  gases  by  a  particles  con- 
sists exclusively  in  the  removal  of  a  single  electron  from  each 
molecule  affected,  thus  leaving  an  equal  number  of  singly  posi- 
tively charged  gaseous  ions,  which  in  the  case  under  consideration 
would  be  H2  or  Oj.  Of  course  there  will  be  a  certain  tend- 
ency  for  immediate  recombination   of  the   electrons   with   the 

"A.  Debierne,  Ann.  de  Physique  (9)  2,  97-127  (1914). 


THE  RADIOCHEMICAL  EFFECTS  117 

oppositely  charged  ions  but  our  general  knowledge  of  the  recom- 
bination of  gaseous  ions  ^^  informs  us  that  its  rate  is  not  exceed- 
ingly great,  and  on  account  of  the  large  excess  of  electrically 
neutral  H2  and  O2  molecules  in  the  gaseous  mixture,  there  will 
be  ample  opportunity  for  the  free  electrons  to  attach  themselves 
to  these  molecules,  forming  negative  ions  H2  or  O2.  The  chemi- 
cal activity  of  ions  may  be  admitted  on  general  grounds,  and 
it  is  therefore  fair  to  assume  that  all  four  kinds  of  ions  can  form 
H2O2  by  combining  with  the  hydrogen  or  oxygen  present.  If  it 
is  then  assumed  that  each  molecule  of  H2O2  retains  its  positive 
or  negative  charge  until  it  is  reduced  by  electrically  neutral 
hydrogen  to  form  two  molecules  of  water  from  each  molecule 
of  H2O2,  we  should  thus  have  as  a  net  result  from  each  original 
pair  of  ions  two  molecules  of  charged  H2O2,  each  of  which  would 
produce  by  combination  with  Hg  two  molecules  of  H2O,  making 
four  molecules  of  HgO  for  each  original  pair  of  ions.  It  has 
already  been  shown  that  Scheuer  found  3.7,  and  that  the  results 
of  Lind  give  a  value  either  slightly  less  (3.5)  or  exactly  four, 
depending  upon  what  assumption  is  made  as  to  the  position 
of  Ra  A  in  the  reaction  vessel  at  the  time  of  its  decay.  A 
value  somewhat  below  4  could  be  explained  by  cross  reactions 
between  charged  molecules;  for  example,  it  could  be  assumed 
that  the  H2O2,  actually  found  as  a  product  of  the  reaction  by 
Scheuer,  had  resulted  from  its  stabilization  by  becoming  electri- 
cally neutralized,  preventing  its  reduction  by  hydrogen.  The 
mechanism  just  proposed  at  least  shows  that  the  ratio  M/N  =  4 
is  still  within  the  limits  of  possible  ionic  explanation  without 
resorting  to  other  theories.  If  it  be  assumed  with  Bodenstein 
(§  55)  that  a  free  electron  can  attach  itself  to  activate  a  molecule, 
is  again  detached  at  the  moment  of  reaction,  and  continues  to 
act  thus  through  a  large  number  of  cycles  until  consumed  by 
some  reaction  in  which  it  is  not  again  liberated,  there  is  almost 
no  limit  to  the  multiple  activity  of  a  single  electron. 

49.    Exceptions  to  Ionic-Chemical  Equivalence — Reactions  in 
Which  M  Exceeds  N. 

By  consulting  the  column  of  M/N  values  given  in  Table  VII, 
§  36,  in  which  M  is  the  number  of  molecules  involved  in  a  given 

".T.   S.  Townsend,  Phil.   Trans.  Roy.  Soc.   193A,   157    (1899).     R.   K.   Mc- 
Clung,  Phil.  Mag.   (6)   3,  283  (1902)  ;  P.  Langevin,  Tliesis  Paris  (1902),  p.  151. 


118  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

chemical  reaction  and  N  is  the  number  of  ions  produced  by  the 
radiation,  it  will  be  observed  that  the  cases  in  which  M  exceeds 
N  fall  into  two  general  classes,  those  in  which  the  M/N  ratio 
lies  between  1  and  4,  and  those  in  which  it  attains  values  of  an 
entirely  different  order  amounting  to  several  thousand.  With 
respect  to  those  values  falling  in  the  former  class  it  has  been 
suggested  in  the  foregoing  paragraph  that  they  do  not  constitute 
real  exceptions,  but  that  by  making  certain  assumptions  as  to 
the  mechanism  ofXhe  reactions,  an  agreement  between  ionization 
and  chemical  action  in  a  sense  concordant  with  Faraday's  Law 
may  still  be  attained.  In  the  case  of  the  reaction  brought  about 
between  hydrogen  and  oxygen  by  a  rays,  such  a  mechanism  was 
proposed  and  discussed  in  detail  in  §  48.  On  account  of  our 
incomplete  knowledge  of  the  entire  behavior  of  gaseous  ions, 
and  also  on  account  of  an  insufficiency  of  exact  experimental 
data,  it  does  not  appear  possible  at  present  to  reach  a  final  deci- 
sion as  to  the  exact  relation  between  gaseous  ionization  and 
chemical  action,  nor  would  it  be  profitable  to  discuss  theoretical 
possibilities  as  to  exact  mechanisms  for  other  reactions.  The 
number  of  possible  variables  exceeds  greatly  the  number  of 
equations  now  available  for  the  solution  of  the  problem. 

Of  the  second  class  of  reactions,  in  which  M  exceeds  N  by  a 
large  quantity,  there  is  at  the  present  time  only  one  example, 
namely,  the  interaction  between  hydrogen  and  chlorine  gases. 
This  particular  reaction  has  also  been  of  great  photochemical  in- 
terest for  more  than  a  generation.  The  classical  experiments  of 
Bunsen  and  Roscoe  ^^  followed  the  work  of  Draper  ^^  in  calling 
attention  to  the  importance  of  this  most  prominent  example  of 
photochemical  action,  and  further  investigation  of  the  various 
phases  of  the  reaction  has  continued  to  the  present  time.  It  has 
been  repeatedly  shown  that  the  activity  of  the  hydrogen-chlorine 
mixture  with  respect  to  light  varies  with  the  purity  of  the  mix- 
ture. The  influence  of  the  impurities  exhibits  itself  in  retarding 
the  rate  of  the  photochemical  action  and  of  lengthening  the  dura*- 
tion  of  the  so-called  "induction  period"  during  which  the  rate  of 

"  R.  Bunsen  and  H.  E.  Roscoe,  Ostumld'a  Klasaiker  Noa.  Si  and  S8  (Leip- 
zig, 1892).  Grig.  Refs.  Pogg.  Ann.  100,  43-88;  481-510;  101.  235-63  (1857); 
ibid.,  108,  193-273    (1859). 

«  Draper,  PhU.  Mag.   (3)  23,  401  (1843). 


THE  RADIOCHEMICAL  EFFECTS  119 

reaction  increases  to  a  maximum.  Chapman  and  MacMahon^* 
have  made  exhaustive  investigations  of  the  inhibition  of  the 
photochemical  interaction  of  hydrogen  and  chlorine.  They  have 
determined  that  oxygen  is  one  of  the  most  effective  inhibitors 
and  that  the  rate  of  reaction  is  inversely  proportional  to  the 
quantity  of  oxygen  present  for  oxygen  contents  from  0.08-1.0% 
by  volume.  They  later  showed  that  ozone  is  a  very  effective 
inhibitor.  These  discoveries  have  a  very  important  bearing  on 
the  theory  advanced  to  explain  the  excessive  action  of  a  rays  on 
the  Hg  —  CI2  mixture. 

As  has  already  been  stated  (p.  85)  the  results  of  Jorissen 
and  Ringer  on  the  combination  of  Hg  +  CI2  under  the  influence 
of  penetrating  rays  enabled  Lind  to  estimate  that  the  M/N  ratio 
exceeded  unity  by  100  to  1000  fold.  This  exceptional  ratio  led 
Bodenstein  and  Taylor  {loc.  cit.)  to  determine  the  effect  of  a 
rays  on  the  same  reaction.  It  was  found  that  the  reactivity  of 
the  mixture  varied  with  its  purity,  as  in  the  case  of  the  photo- 
reaction,  and  that  in  a  mixture  of  maximum  sensitiveness  at 
least  4000  molecules  of  Hg  and  Clg  combine  for  one  pair  of  ions 
formed.  As  will  be  shown  in  the  following  chapter,  Bodenstein 
calculated  that  the  rate  of  the  photochemical  interaction  of  H2 
and  CI2  exceeds  the  predictions  of  Einstein's  photochemical 
equivalence  law  by  a  factor  of  about  10®.  Bodenstein  was  led 
to  propose  an  electronic  theory  for  photochemical  action  accord- 
ing to  which  an  electron  primarily  liberated  by  any  form  of 
radiation  can  successively  activate  a  large  number  of  chlorine 
molecules,  which  then  react  with  hydrogen,  again  liberating  the 
electron  at  the  time  of  reaction.  This  process  would  continue 
indefinitely  from  even  a  small  number  of  initial  free  electrons 
except  for  the  fact  that  finally  the  electron  activates  a  foreign 
molecule  (Chapman's  inhibitors)  and  is  not  again  liberated  by 
the  reaction.  Bodenstein  assumed  oxygen  to  be  the  inhibitor  in 
this  case  and  that  the  ozone  formed  again  decomposes  to  give 
oxygen.  This  fits  with  a  number  of  other  observations,  namely, 
the  inhibitive  effect  of  oxygen  and  of  ozone  actually  observed  by 
Chapman  and  MacMahon,  and  with  the  observation  of  Lind 
that  ozone  formation  is  statistically  equivalent  to  the  ionization, 
from  which  it  follows  that  the  free  electrons  are  consumed  in  the 
reaction.    It  also  explains  why  the  reaction  does  not  proceed  after 

"D.  L.  Chapman  and  P.  S.  MacMahon,  Joum.  Chem.  Soc.  Lond.  95j,  959-04  ; 
95ii,  1717-20   (1909)  ;  97^,  845-51   (1910). 


120  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

cessation  of  the  radiation.  As  will  be  seen  later,  Bodenstein  had 
to  abandon  the  theory  as  applied  to  photochemical  action  of 
chlorine  gas  on  account  of  the  lack  of  ionization  which  he  had 
assumed;  but  in  the  case  of  the  action  as  produced  by  a  parti- 
cles where  we  have  actual  ionization,  his  theory  remains  appli- 
cable, in  principle  at  least,  to  explain  the  abnormally  high  value 
of  the  M/N  ratio.  As  alternative  theories  we  shall  have  that  of 
Nernst  for  the  photochemical  interaction  Hg  +  Clg  and  the  later 
one  of  Bodenstein,  both  of  which  will  be  presented  in  the  follow- 
ing chapter.  The  fact  that  the  Hg  +  Bvr,  mixture  at  ordinary 
temperature  is  not  photo-sensitive  and  that  its  M/N  value  for  a 
radiation  is  normal  is  of  much  interest. 

50.    Exceptions  to  Ionic-Chemical  Equivalence.    Reactions  in 
Which  N  Exceeds  M. 

A  study  of  the  M/N  ratios  for  various  reactions  in  Table  VII, 
§  36,  shows  that  the  cases  in  which  the  ratio  drops  below  unity 
may  be  divided  into  those  where  the  departure  from  unity  is 
not  below  0.5,  and  those  where  considerably  lower  values  are 
attained.  The  case  of  slight  departures  needs  no  further  dis- 
cussion; the  agreement  may  be  regarded  as  satisfactory  from 
the  data  at  present  available.  The  small  deviations  might  be 
explained  either  on  ionic  grounds  or  by  the  assumption  of  some 
recombination  to  form  the  original  product,  thus  reducing  the 
reaction  efficiency. 

The  cases  in  which  the  M/N  ratio  drops  to  much  lower  values 
seem  to  divide  themselves  into  two  classes,  those  where  difference 
in  state  of  aggregation  is  the  controlling  factor,  and  those  in 
which  the  inherent  properties  of  the  reaction  itself  produce  the 
low  rate. 

In  the  case  of  the  decomposition  of  water  it  is  very  evident 
that  the  state  of  aggregation  plays  a  large  role.  It  has  been 
shown  in  §  37  from  the  results  of  Duane  and  Scheuer  that,  while 
water  in  the  liquid  state  is  readily  decomposed  by  a  radiation 
in  almost  exactly  the  quantity  required  by  ionic-chemical 
equivalence  (or  by  electrolysis),  the  decomposition  of  ice  un- 
der the  same  conditions  is  only  about  5%  of  that  of  water. 
While  for  water  vapor  for  the  same  amount  of  a  radiation 
absorbed,  the  decomposition  showed  variable  values  somewhat 


THE  RADIOCHEMICAL  EFFECTS  121 

lower  yet  than  those  for  ice.  On  the  other  hand  Wourtzel  (§  39) 
found  that  the  decomposition  of  solid  HgS  at  —190°  was  of  the 
same  order  as  found  for  the  gas  at  18°.  This  does  not  necessarily 
mean  that  the  decomposition  of  gaseous  and  solid  HgS  at  the 
same  temperature  would  be  equal,  since  Wourtzel  found  the  rate 
of  decomposition  of  the  gas  at  higher  temperatures  to  have  a 
marked  negative  temperature  coefficient,  which,  if  continued  to 
lower  temperatures,  might  mean  that  the  decomposition  of  the 
gas  at  —190°  would  be  (were  it  possible  to  determine  it  at  this 
temperature)  much  higher  than  at  18°.  It  is  difficult  to  find  a 
plausible  explanation  for  the  results  for  water  vapor  and  ice.  In 
the  case  of  water  vapor  one  would  be  inclined  to  attribute  the  low 
value  to  recombination  owing  to  the  greater  mobility  of  the  sys- 
tem, but  one  is  confronted  with  the  case  of  ice,  where  mobility 
must  be  at  a  minimum,  and  yet  the  decomposition  is  much  lower 
than  that  of  water.  The  explanation  might  be  entirely  through 
temperature  effect.  This  would  require  a  maximum  at  ordinary 
temperature  for  the  rate  of  decomposition  of  water.  While 
Wourtzel  has  observed  a  minimum  for  NgO  at  ordinary  tem- 
perature, no  maxima  have  yet  been  found.  Since  the  tempera- 
ture coefficients  themselves  remain  unexplained,  speculation  in 
this  direction  is  not  illuminating. 

To  return  to  a  consideration  of  gases,  Wourtzel  found  in  the 
case  of  CO,  but  slight  decomposition,  which  he  attributed  to  the 
greater  stability  of  this  compound,  in  other  words,  to  the  excessive 
amount  of  energy  necessary  to  bring  about  its  decomposition. 
Such  a  view  is  not  in  accord  with  the  ionization  theory  of  the 
reactions,  since  we  know  that  CO2  is  readily  ionized  by  a  par- 
ticles and  that  the  amount  of  energy  expended  in  producing  its 
ionization  is  greatly  in  excess  of  that  necessary  for  its  chemical 
decomposition.  As  will  be  seen  in  the  following  section,  there 
does  appear  to  be  some  tendency  for  reactions  proceeding  in  the 
direction  of  the  chemical  free  energy  to  utilize  a  greater  propor- 
tion of  the  kinetic  energy  of  a  radiation  than  do  those  taking 
place  opposed  to  the  free  energy.  But  among  those  of  the  latter 
class  there  is  no  distinct  tendency  for  the  reaction  to  be  controlled 
by  this  factor,  and  it  is  very  certain  that  the  failure  of  the 
decomposition  of  CO2  gas  by  a  rays  is  not  due  to  lack  of  the 
necessary  kinetic  energy  or  of  ability  of  CO2  to  absorb  it,  as  evi- 
denced by  the  ionization. 


122  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

The  question  of  the  chemical  action  of  a  rays  on  solids  has 
not  been  very  thoroughly  examined  experimentally.  As  pointed 
out  in  §§  28  and  36,  the  decomposition  of  some  of  the  halides  of 
the  alkalis  and  alkaline  earths  has  been  investigated  with  pene- 
trating radiation  and  found  to  be  very  small,  in  some  cases 
almost  zero.  It  is  very  fortunate  that  all  solid  substances  are 
not  attacked  and  chemically  changed  by  radium  radiations,  as 
it  would  be  impossible  to  carry  out  manometric  measurements 
in  glass  or  other  vessels  or  to  determine  the  true  volume  of 
radium  emanation,  if  gases  like  oxygen,  for  example,  were  being 
continually  liberated  from  the  glass  wall.  There  is  no  evidence 
of  such  being  the  case.  Radium  emanation  may  be  retained  in 
glass  without  the  production  of  measurable  quantities  of  pres- 
sure. It  is  very  desirable  to  extend  the  investigation  of  the 
chemical  effects  of  a  rays  to  other  solid  substances  both  crys- 
talline and  colloidal. 

It  is  interesting  to  point  out  that  no  great  deviations  have  yet 
been  observed  of  the  M/N  value  for  reactions  of  any  substances 
in  the  liquid  state,  that  the  deviations  in  the  solid  state  are  all 
in  the  direction  of  low  values  of  M/N,  while  in  the  gaseous  state 
we  have  examples  of  large  deviations  from  unity  in  both 
directions. 

51.    Energy  Utilization  of  a  Rays  in  Chemical  Reactions. 

In  the  last  column  of  Table  VII,  §  36,  are  estimates  of  the 
percentage  of  the  total  energy  of  the  a  rays  absorbed  in  a  given 
system  which  is  utilized  by  the  resulting  chemical  action.  The 
values  have  direct  significance  only  in  the  cases  where  the  reac- 
tion produced  is  opposed  to  the  chemical  free  energy  and  there- 
fore requires  the  expenditure  of  external  energy.  Values  are 
also  given,  however,  for  the  reactions  proceeding  with  the  chemi- 
cal energy,  in  order  to  show  that  with  the  one  large  exception 
of  the  hydrogen-chlorine  reaction,  and  to  a  much  less  degree 
that  of  hydrogen-oxygen  combination,  the  order  of  the  values  is 
not  very  different  from  those  of  reactions  opposed  to  the  chemical 
free  energy.  This  indicates  that  the  chemical  free  energy  does 
not,  at  ordinary  temperature,  play  an  important  part  in  reactions 
produced  by  a  particles.  In  other  words,  it  appears  necessary 
to  do  work  on  the  molecules  to  render  them  chemically  active, 


I 


THE  RADIOCHEMICAL  EFFECTS  123 

and  from  the  low  energy  utilization,  it  is  evident  that  the  work 
of  the  primary  action  involves  energy  quantities  very  much  in 
excess  of  the  net  chemical  energy,  and  that  the  amount  of  energy 
necessary  to  do  this  work  is  of  the  same  order,  whether  the  reac- 
tion is  proceeding  with  or  opposed  to  the  chemical  energy.  If 
ionization  is  the  intermediate  step  involved,  this  is  just  what 
would  be  expected.  Since  the  energy  necessary  to  form  a  pair 
of  ions  (5.5.10"^^  ergs)  is  large  compared  with  the  chemical 
energy  of  reaction  referred  to  a  single  molecule,  the  energy  trans- 
formation will  be  small.  For  example,  if  the  M/N  value  is  unity 
for  a  reaction  of  which  Q  =  100  Cals.,  q  or  the  heat  of  reaction 
referred  to  a  single  molecule  would  be  6.10~^^  ergs,  and  the  energy 
utilization  would  be  about  10%. 

For  most  of  the  reactions  where  expense  of  energy  is  actually 
required  the  utilization  factor  is  about  2%  or  less.  Warburg  ^^ 
has  pointed  out  that  a  low  order  of  energy  transformation  is  one 
of  the  chief  characteristics  of  photochemical  action.  Warburg 
explains  this  by  the  assumption  of  a  primary  reaction  consisting 
in  splitting  the  molecules  into  atoms,  a  process  that  would  require 
much  more  energy  than  that  involved  in  the  finally  resulting 
chemical  reaction,  were  it  wholly  molecular  in  mechanism.  It 
does  not  appear  at  all  impossible  that  free  atoms  are  the  inter- 
mediate products  in  photochemical  reactions,  while  free  ions  and 
electrons  may  be  the  intermediate  products  or  agents  in  reactions 
produced  under  ionizing  conditions. 

It  might  be  mentioned  that  the  values  for  energy  transforma- 
tion given  in  the  last  column  of  Table  VII  vary  considerably  in 
reliability.  The  later  values  for  water  formation,  and  for  decom- 
position of  water,  ammonia,  hydrogen  sulfide,  and  nitrogen  pro- 
toxide may  be  accepted  with  assurance.  The  data  involved  in 
most  of  the  other  cases  are  older  and  perhaps  should  be  verified 
before  they  can  be  accepted  with  the  same  degree  of  certainty. 

52.    Chemical  Action  Produced  by  Electrical  Discharge  in 
Gases. 

The  subject  of  the  chemical  effects  of  electrical  discharge 
through  gases  is  too  large  to  be  considered  in  its  entirety  within 
the  limits  of  the  present  work.     Attention  will  be  confined  to 

"l*:.  Warburg,  Sitzb.  Aka(l.  Wi^s.  Berlin,  pp.  746-64    (X9XX), 


124  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

those  phases  of  the  subject  which  are  more  closely  related  to 
radiochemistry  and  to  the  ionic  theory  of  gas  reactions. 

As  soon  as  it  had  been  shown  that  ozone  formation  from  oxy- 
gen is  proportional  to,  and  probably  statistically  equal  to,  the 
ionization  (§33)  both  in  the  cases  of  a  radiation  and  certain 
kinds  of  electronic  discharge,  the  application  of  the  same  princi- 
ple to  the  broader  field  of  ozone  formation  by  silent,  spark,  and 
other  forms  of  electrical  discharge,  followed  naturally.  Theories 
were  independently  proposed  by  Kabakjian,^^  by  Lind,^^  and  by 
Kriiger  ^^  which  were  practically  identical.  The  generalization 
was  made  that  probably  in  all  cases  ozone  formation  in  gaseous 
oxygen  is  the  result  of  the  primary  ionization  of  oxygen  by  some 
form  of  electronic  discharge.  The  quantity  of  ionization  involved 
in  the  ozone  formation  is  not  directly  related  to  the  flow  of  cur- 
rent, but  is  the  far  greater  number  of  ions  produced  in  the  gas 
by  electronic  shock  (§  16),  which  never  reach  the  electrodes  and 
therefore  take  no  part  in  the  electrical  conduction,  since  the 
intensity  of  ionization  far  exceeds  the  limiting  conditions  for 
attaining  saturation  current.  This  predicts  that  the  quantity  of 
ozone  formed  should  not  be  related  to  the  current  flowing,  as 
required  by  direct  application  of  Faraday's  Law,  but  should  be 
a  much  greater  quantity.  The  experiments  of  Warburg  ^^  on 
ozone  formation  by  silent  discharge  confirm  this  fully.  Under 
some  conditions  Warburg  found  that  about  one  thousand  fold 
as  much  ozone  is  formed  as  would  correspond  to  the  current,  or 
that  instead  of  the  theoretical  96,500  coulombs  required  per 
chemical  equivalent,  less  than  100  coulombs  suffice  for  the  pro- 
duction of  one  gram-equivalent  of  ozone.  Hitherto  it  has  not 
been  possible  to  confirm  the  theory  that  the  total  ozone  forma- 
tion would  be  accounted  for  by  the  ionization  by  electronic 
shock,  because  we  have  no  means  of  measuring  the  total  ioniza- 
tion produced.  Conversely  the  conditions  under  which  ioniza- 
tion by  shock  have  been  measured  ^"  are  not  suitable  for  the 
formation  and  measurement  of  ozone. 

Recently  the  subject  of  ozone  formation  in  corona  discharge 

»D.  H.  Kabakjian,  Phys.  Rev.,  31,  122-35   (1910). 
»»S.  C.  Lind,  Trans.  Amcr.  Electrochem.  Soc,  21,  181-3  (1912) 
"F.  Krugor,  Phya.  Zcit.,  13,  1040-3  (1912). 

"B.   Warburg,   Sitzh.   Akad.    Wi88.    Berlin,   p.   1011    (1903);    ibid.,   p.    1228 
(1904).     Ann.  d.  Physik  20,  734-42   (190G)  ;  ibid.,  20.  751  ct  aeq.   (190G). 
"  See  tbe  dlsgusslop  of  Townse«d"s  work  in  Chapter  4. 


I 


THE  RADIOCHEMICAL  EFFECTS  125 

has  been  investigated  by  Anderegg  ^^  and  by  Rideal  and  Kunz.^^ 
Anderegg  expresses  the  opinion  that  oxygen  atoms  are  probably 
present  in  all  cases  of  ozone  formation,  but  defers  judgment  as 
to  whether  ozone  is  formed  from  oxygen  ions.  Rideal  and  Kunz 
have  paid  especial  attention  to  the  distribution  of  ozone  in  the 
direct  current  corona  of  positive  or  negative  sign.  Their  meas- 
urements of  the  quantity  of  ozone  were  made  by  two  independent 
methods,  chemical  and  photometrical.  While  the  quantities  of 
ozone  formed  in  the  positive  and  in  the  negative  corona  are 
approximately  the  same,  the  distribution  differs  in  a  marked  man- 
ner in  the  two  cases.  The  various  ways  in  which  ozone  can  be 
formed  in  the  light  of  the  radiation  hypothesis  (see  following 
chapter)  were  also  reviewed  by  Rideal  and  Kunz,  and  the  con- 
clusion drawn  that  molecules  of  one  kind  can  be  activated  by 
radiation  to  different  extents. 

The  combination  of  electrolytic  hydrogen  and  oxygen  under 
the  influence  of  electrical  discharge  has  been  investigated  by 
Kirkby.^^  The  experimental  conditions  were  regulated  sq  as  to 
"parallel  those  employed  by  Townsend  (§§  16  and  18)  in  his 
studies  of  ionization  by  collision.  Very  low  gas  pressures  (a 
few  mms,  of  Hg)  were  used.  The  distance  between  the  electrodes 
was  varied  from  about  0.25  to  nearly  2  cms.  Kirkby  found  that 
the  rate  of  combination  is  proportional  to  the  current  passing, 
and  that  about  4  molecules  of  HgO  are  formed  per  pair  of  ions. 
It  is  very  interesting  to  observe  that  this  number  is  the  same  as 
that  obtained  by  Lind  (and  practically  the  same  as  that  of 
Scheuer)  (loc.  cit.  §  48)  for  the  same  reaction  under  the  influence 
of  a  particles.  Kirkby  concluded  that  hydrogen  molecules  react 
with  uncharged  oxygen  atoms,  which  are  dissociated  by  collision 
with  electrons  under  certain  conditions.  Only  one  half  of  the 
collisions  of  electrons  with  the  necessary  velocity  actually  results 
in  the  dissociation  of  the  oxygen  molecule.  For  the  action 
within  the  positive  column  Kirkby  proposed  a  general  formula: 
Njj  Q  =  7.9p.e-*2-^p/Y,  in  which  p  is  the  pressure  in  mms.  and 
Y  is  volts.cm-\  The  applicability  of  the  formula  is  independent 
of  the  apparatus. 

a^F.  O.  Anderegg,  Journ.  Amer.  CTiem.  Soc.  39,  2581-95   (1917). 
22 E.  K.  Rideal  and  J.  Kunz,  Journ.  Phys.  Chem.  24,  379-93  (1920). 
=3  p.    J.    Kirkby,   Phil.   Mag.    (6)    7,    223-32    (1904);    9,    171-85    (1905);    13, 
289-312  (1907)  ;  Proc.  Roy.  Sqc.  85A,  151-74  (1911), 


126  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

Among  other  gas  reactions  produced  by  electrical  discharge 
may  be  mentioned  the  very  careful  investigation  by  Davies  ^* 
in  LeBlanc's  laboratory  at  Leipzig  of  the  decomposition  and 
formation  of  ammonia  in  a  Siemens  tube.  Davies  investigated 
the  reaction  and  equilibrium  from  the  standpoint  of  the  applica- 
tion of  the  mass  action  law.  He  found  that  the  course  of  the 
reaction  may  be  expressed  by  a  first  order  equation,  that  the 
rate  of  decomposition  is  approximately  proportional  to  the  cur- 
rent strength,  and  that  the  rate  of  decomposition  has  a  very  small 
temperature  coefficient,  the  rate  at  100°  being  double  that  at 
ordinary  temperature.  Excess  of  hydrogen  was  found  to  lower 
the  rate  of  decomposition,  while  excess  of  nitrogen  increased  it. 
Equilibrium  attainable  from  both  directions  was  almost  inde- 
pendent of  the  current  strength  and  corresponded  to  ammonia 
formation  to  the  extent  of  6%  of  the  maximum  possible.  With 
excess  of  either  component  the  equilibrium  changes  in  favor  of 
further  ammonia  decomposition.  The  law  of  mass  action  is  not 
applicable  to  the  equilibrium.  The  rate  of  ammonia  formation 
decreases  slightly  in  excess  of  nitrogen  and  increases  slightly  in 
excess  of  hydrogen;  this  result  is  in  accord  with  those  for  influ- 
ence of  excess  on  the  decomposition,  but  are  not  those  that  would 
be  expected  by  analogy  with  influence  of  excess  of  components 
in  water  formation  by  a  rays  (§  45),  where  the  excess  of  lighter 
gas  diminished  the  rate  while  excess  of  the  heavier  increased  it. 
Falckenberg  ^^  and  Pohl  2«  have  studied  the  decomposition  of 
ammonia  in  a  Siemens  tube  rather  from  the  physical  and  elec- 
trical standpoint  and  find  Faraday's  law  inapplicable  to  the  rela- 
tion between  current  flowing  and  quantity  of  ammonia  decom- 
posed. From  what  has  been  said  previously  in  regard  to  ozone 
formation  it  is  evident  that  one  should  not  expect  any  direct 
relation  between  the  two.  To  make  the  statement  more  general 
it  is  quite  as  unreasonable  to  expect  equivalence  between  the 
current  flowing  and  the  chemical  effect  in  the  case  of  electrical 
discharge  through  gases,  as  it  would  be  to  expect  equivalence 
between  the  total  primary  charge  of  a  rays  and  their  chemical 
effects.  In  both  cases  equivalence  must  be  sought  in  the  far 
greater  number  of  ions  produced  by  collision. 

»*J.  H.   Davies,  Zeit.  phys.   Chem.  64,   657-85    (1908).     M.   LeBlanc,   Verh. 
Sachs.  Qea.  W<««.,  Leipzig,  60,  3S-63   (1014). 
3»  Falckenberg,  Thesis,  Berlin  (1006). 
"XI.  Pohl,  Ann.  d.  Physik  (4)  21,  879  (1906), 


THE  RADIOCHEMICAL  EFFECTS  127 

Further  consideration  of  the  experimental  data  on  the  chemi- 
cal effects  of  the  passage  of  electrical  discharge  through  gases  is 
not  within  the  scope  of  this  work.^^  In  its  most  general  aspects 
the  subject  may  be  regarded  as  having  great  scientific  and  per- 
haps important  commercial  possibilities  which  are  well  worthy  of 
further  research.  For  example,  the  possibility  of  an  electro- 
chemical process  in  which  only  100  coulombs  are  required  for 
the  production  of  one  chemical  equivalent  ought  to  prove  attrac- 
tive to  the  electrochemical  engineer,  provided  the  energy  rela- 
tions should  not  prove  to  be  too  unfavorable. 

Besides  the  reactions  produced  by  electrical  discharge  in  gases 
at  ordinary  pressure  there  is  a  class  of  reactions  observed  at  low 
pressures  which  may  or  may  not  be  of  chemical  nature.  The 
''clean  up"  of  gases  in  spectrum  tubes  has  been  observed  for 
many  gases,  but  is  especially  puzzling  for  the  gases  of  the  inert 
series  where  we  can  not  assume  ordinary  chemical  reactions  to 
take  place.  Although  a  mechanical  or  electrical  explanation, 
such  as  that  discussed  for  the  hardening  of  X  ray  tubes  (§§  16 
and  18)  might  be  proposed,  Collie  ^^  has  recently  observed  the 
clean  up  of  pure  xenon  in  a  manner  very  puzzling  to  explain. 
Xenon  differs  from  the  other  inert  gases  in  that  heating  does  not 
again  liberate  it  from  the  electrode  or  "splashed"  mirror  sur- 
rounding the  electrode.  Using  platinum,  aluminum  and  copper 
electrodes.  Collie  cleaned  up  more  than  2  c.  c.  of  xenon,  of  which 
he  was  unable  to  recover  more  than  a  few  per  cent  even  by  chemi- 
cally dissolving  the  electrodes,  the  mirror  and  the  glass  spectrum 
tube  itself.  Collie  was  almost  forced  to  conclude  that  xenon 
had  entered  into  some  form  of  chemical  combination  from  which 
it  was  not  liberated  as  gas  by  the  radical  treatment  employed. 
Radium  emanation  has  been  found  by  several  authorities  ^^  to  be 
cleaned  up  in  a  spectrum  tube  in  a  similar  way.  Since  radium 
emanation  can  always  be  detected  by  its  y  radiation  it  would  be 
very  interesting  to  repeat  the  experiments  of  Collie  employing 
emanation  instead  of  xenon  to  ascertain  if  any  light  would  be 
thrown  upon  the  nature  of  the  "clean  up." 

The  Research  Staff  of  the  General  Electric  Company  of  Lon- 

27  References  to  the  literature  will  be  found  in  the  paper  of  Davies  (loc. 
cit.). 

'"J.  N.  Collie,  Proc.  Roy.  Soc.  97A,  349-54   (1920). 

2«  Rutherford,   "Radioactive   Substances"    (1913),   p.   482. 


128  THE  CHEMICAL  EFFECTS   OF  ALPHA  PARTICLES  AND  ELECTRONS 

don  recently  presented  ^°  the  results  of  an  investigation  of  the 
disappearance  of  gas  in  the  electric  discharge,  from  which  it 
appears  that  the  phenomenon  is  closely  connected  with  the 
appearance  of  a  glow  in  the  discharge  tube,  which  is  believed  to 
result  from  a  reversible  chemical  action. 

53.    Production    of    Free    Electrical    Charges    by    Chemical 
Action. 

Related  to  the  question  of  the  production  of  chemical  action 
by  ionization  is  the  converse  one  as  to  the  liberation  of  charges 
by  chemical  reaction.  Various  opinions  have  been  expressed  as 
to  the  reality  of  this  phenomenon.  There  can  be  no  question 
but  that  chemical  action  is  often  accompanied  by  the  liberation 
of  electrical  charges,  but  whether  or  not  this  is  ever  true  in  a 
homogeneous  gaseous  system  where  there  is  no  possibility  of  the 
accompanying  influence  of  high  temperature  or  of  some  physical 
process,  requires  careful  consideration. 

By  introducing  a  gold  leaf  electroscope  directly  into  a  mix- 
ture of  hydrogen  and  chlorine  gases  and  causing  them  to  react 
under  the  stimulation  of  light,  J.  J.  Thomson  ^^  showed  most 
conclusively  that  no  free  charges  are  produced  either  in  the 
"induction  period"  or  during  vigorous  reaction.  X  rays  pro- 
jected intq  the  same  system  caused  the  gold  leaf  to  discharge, 
proving  its  sensitiveness,  but  failed  to  increase  the  rate  of  com- 
bination of  hydrogen  and  chlorine  as  observed  by  the  Bunsen 
and  Roscoe  actinometer.  It  might  be  mentioned  parenthetically 
that  this  does  not  prove  that  X  rays  do  not  cause  hydrogen  and 
chlorine  to  react  (proportionately  to  the  ionization),  since  the 
sensitiveness  of  the  gold  leaf  discharge  to  detect  ions  and  that 
of  the  Bunsen  and  Roscoe  actinometer  to  detect  the  disappear- 
ance of  molecules  by  diminution  in  volume  are  of  a  wholly  dif- 
ferent order.  Klimmell  ^^  later  thought  he  had  found  evidence 
contrary  to  that  of  Thomson,  but  Thomson's  result  was  con- 
firmed by  a  very  careful  investigation  by  LeBlanc  and  Vollmer,^^ 

'ophil  Mag.  (6)  40,  585-611  (1920).  (Conducted  by  N.  R.  Campbell  and 
J.  W.  II.  Ryde.) 

»» J.  J.  Thomson,  Proc.  Camb.  Phil.  Soc,  11,  90  (1901)  ;  "Conduction  of 
Elect.  Through  l/ases,"  2nd  Edit.,  p.  229. 

«»G.  Kunimcll,  Zeit.  Klcktrochem.  17.  409    (1911). 

"M.  LeBlanc  and  M.  Vollmer,  ibid.,  20,  494-7   (1914). 


1 


THE  RADIOCHEMICAL  EFFECTS  129 

who  also  demonstrated  for  the  first  time  a  chemical  effect  of 
X  rays  in  a  gas  reaction  (H2  +  CI2). 

On  the  other  hand  Haber  and  Just^*  have  demonstrated  in 
an  extended  series  of  experiments  that  the  action  of  certain  gases, 
including  water  vapor,  the  halides  and  phosgene,  on  alloys  or 
amalgams  of  the  alkali  metals  results  in  charging  the  metal 
positive  owing  to  the  liberation  of  electrons  from  its  surface. 
Haber  and  Just  demonstrated  that  temperature  has  an  influence; 
iodine  vapor  at  —79°  C.  had  no  effect,  while  at  +3°  there  was 
an  effect  which  became  strong  at  +13°.  They  showed  that  the 
combined  effect  of  light  and  chemical  action  emits  more  electrons 
than  the  sum  of  the  separate  emissions.  Other  metals  than  the 
alkalis  show  an  effect  if  the  temperature  be  raised.  Aluminium 
begins  to  show  an  effect  at  180°,  which  becomes  rapid  at  240°. 
The  unipolarity  of  the  effect  begins  to  disappear  at  higher  tem- 
peratures. Amalgams  of  Cs,  K,  and  Li  gave  negative  ions 
instead  of  electrons.  The  quantities  of  electricity  emitted  were 
far  below  Faraday  equivalence;  for  example,  the  formation  of 
one  gram-molecule  of  KCl  was  associated  with  an  emission  cor- 
responding to  65  coulombs  instead  of  96,500. 

In  a  study  of  the  oxidation  of  metallic  Na,  K  and  alkaline 
earths,  Reboul  ^^  showed  that  the  electrical  effects  accompany- 
ing these  reactions  are  weak  and  difficult  to  detect  when  the 
reaction  is  unaccompanied  by  some  purely  physical  phenomenon 
such  as  emission  of  light,  high  temperature,  etc.  Nevertheless 
he  does  not  think  we  are  justified  in  discarding  the  idea  that 
ionization  may  accompany  all  chemical  action.  Bloch  ^^  has 
repeated  some  of  the  earlier  gas  experiments  of  Reboul  ^^  and 
concludes  that  for  the  reaction  NH3  +  HCl,  ionization  is  doubt- 
ful; that  none  is  produced  by  the  reactions:  2NO2  +  0;  SO2  +  O 
(contact  method) ;  H2  +  S;  S  +  O2;  and  decomposition  of  AsHg. 
Only  the  case  2P  +  50  gave  ionization.  Pinkus  ^^  employ^  an 
electroscopic  method  for  two  reactions :  for  2N0  +  O2  he  found  no 
ionization ;  for  the  reaction  NO  +  Clg  no  ionization  was  found  for 

8*F.  Haber  and  G.  Just,  Ann.  d.  Phys.  (4)  30,  411-15  (1909)  ;  Zeit.  Elektro- 
chem.,  10,  275-9  (1910)  ;  17,  592  (1911)  ;  20,  483-5  (1914)  ;  Ann.  d.  Phys.  (4) 
36,  308-40  (1911). 

s'G.  Reboul,  Le  Eadium,  8,  370-81   (1911). 

38  L.  Bloch,  Comp.  rend.  149,  278-9  (1909)  ;  Ann.  de  phys.  ct  chim.,  22,  370- 
417;  441-495    (1911). 

"G.  Reboul,  Comp.  rend.  149,  110-3   (1909). 

"8  A.  Pinkus,  Journ.  de  CJiim.  Phys.  16,  201-27   (1918). 


130  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

equivalent  quantities  nor  for  small  excesses  of  either  gas,  but 
for  large  excess  of  NO  some  ionization  appeared  to  occur. 
Broglie  and  Brizard  ^^  concluded,  after  an  exhaustive  study  of 
the  evidence,  that  chemical  action  produces  ionization  only 
when  accompanied  by  a  physical  reaction  such  as  passage  of  a 
gas  through  liquid,  breaking  a  crystalline  surface,  luminescence, 
etc.  They  state  that  there  is  no  ionization  in  the  case  of  reactions 
of  the  following  classes:  (1)  Between  gases  in  the  cold;  (2)  double 
decomposition  in  liquids;  (3)  dry  decomposition  of  amorphous 
substances  at  slightly  elevated  temperature;  (4)  rupture  of  an 
inactive  surface  by  bubbling.  While  there  is  ionization  in  the 
following  cases:  (1)  Gases  prepared  by  wet  way;  (2)  vigorous 
reactions  by  projection  into  water;  (3)  dry  actions  accompanied 
by  the  decrepitation  of  crystals;  (4)  2Na  +  0  (moist),  feeble 
ionization;  (5)  reactions  with  incandescence,  such  as  flames,  or 
combustion  of  metals  in  Og  or  Cl^',  (6)  reactions  with  lumines- 
cence, such  as  the  oxidation  of  P  and  of  quinine  sulfate. 

The  case  may  be  summed  up  by  stating  that  we  have  no 
definite  evidence  as  yet  of  the  production  of  ionization  or  the 
setting  free  of  electrical  charges  by  any  homogeneous  gas 
reaction  at  ordinary  temperature,  but  that  in  the  case  of  hetero- 
geneous reactions  or  gas  reactions  at  higher  temperature  we  have 
undoubted  cases  of  the  liberation  of  charges,  which  may,  how- 
ever, not  be  directly  the  result  of  the  chemical  action,  but  the 
secondary  result  of  some  accompanying  physical  occurrence. 

The  determination  of  ionization  produced  in  gaseous  explo- 
sions has  been  undertaken  by  Haselfoot  and  Kirkby  ^^  for  elec- 
trolytic hydrogen  and  oxygen  at  80  mm.  pressure,  and  for 
ozoimide  (HN3)  by  Kirkby  and  Marsh.*^  In  the  former  case 
the  M/N  ratio  was  about  10^  and  in  the  latter  about  100  times 
smaller.  The  explosion  method  has  the  disadvantage  that  what- 
ever charges  are  liberated  by  the  reaction  are  produced  suddenly 
in  large  quantity  so  that  the  attainment  of  saturation  current 
might  be  very  difficult.  However,  from  the  small  N/M  ratio 
found  it  may  be  fairly  concluded  that  the  total  liberation  of 
charge  is  small  compared  with  the  number  of  molecules  reacting, 

»»M.  Broglie  and  L.  Briznrd.  Le  Radium  7,  1G4-9  (1910). 

«E.  E.  Haselfoot  and  P.  J.  Kirkl)y,  Phil.  Mag.   (G)   8,  471-81   (1904). 

*ip.  J.  Kirkby  and  J.  E.  Marsh,  Proc.  Roy.  Soc.  87A,  90-99  (1913). 


THE  RADIOCHEMICAL  EFFECTS  131 

because,  if  N  were  anything  like  the  same  order  of  magnitude  as 
M,  the  fields  used  would  have  drawn  a  greater  number  of  ions 
than  was  observed  to  the  electrodes  before  recombination  could 
have  occurred. 


Chapter  10. 
Photochemical  Equivalence  Law. 

54.    Einstein's  Application  of  the  Quantum  Theory  to  Photo- 
chemical Action. 

The  inclusion  of  this  subject,  which  does  not  properly  form 
a  part  of  the  present  monograph,  has  a  two-fold  object:  (1)  to 
enable  a  comparison  between  certain  points  of  similarity  which 
this  branch  of  photochemistry  shares  with  the  other  radiochemi- 
cal effects  which  have  been  discussed  in  the  foregoing  chapters; 
and  (2)  to  present  the  experimental  investigations  which  have 
been  brought  to  bear  upon  a  test  of  the  photochemical  equivalence 
law  since  the  appearance  of  the  standard  works  on  photo- 
chemistry. 

It  has  been  recognized  by  physicists  for  some  time  that  the 
idea  of  the  continuity  of  light  as  expressed  by  Maxwell's  theory 
suffices  for  the  explanation  of  optical  phenomena,  but  that  cer- 
tain other  phenomena,  such  as  ionization  by  light,  photolumi- 
nescence,  and  "dark  radiation,"  require  the  introduction  of  an 
atomistic  conception  of  radiant  energy.  This  step  was  taken  by 
Planck  in  his  quantum  theory  according  to  which  energy  is 
radiated  or  absorbed  only  in  integral  units  equal  to  hv,  in  which 
h  is  the  Planck's  constant  (6.547  x  10"^^  erg.  sec.)  and  v  is  the 
frequency  of  vibration.  Einstein  ^  has  proposed  the  application 
of  Planck's  quantum  theory  to  photochemical  phenomena  in  the 
following  form:  N  =  Q/hv,  in  which  Q  is  the  absorbed  heat 
required  for  the  production  of  the  chemical  action,  N  is  the 
number  of  molecules  dissociated  by  light  of  the  frequency  v. 

In  attempting  to  apply  Einstein's  law  to  actual  photochemical 
reactions  it  is  necessary  to  keep  in  mind  that  it  applies  only  to 
the  primary  light  reaction.  As  will  be  seen  later,  secondary 
reaction  may  intervene  in  such  a  way  that  the  total  quantity 

»A.  Einstein,  Ann.  d.  Physik  (4)  37,  832-8;  38,  881-4;  888  (1912).  Aiso 
ma.   (4)   17,  132-48  (1905). 

132 


PHOTOCHEMICAL  EQUIVALEifCE  LAW  133 

of  chemical  action  resulting  from  the  primary  action  may  be 
either  equivalent  to  it,  or  greatly  in  excess  or  deficiency,  depend- 
ing upon  circumstances.  In  general  it  is  not  possible  to  measure 
the  quantity  of  primary  reaction  directly,  but  only  through  the 
production  of  some  secondary  reaction.  In  order,  therefore,  that 
the  test  of  the  equivalence  required  by  Einstein's  photochemical 
law  shall  have  any  significance  it  is  necessary  to  be  able  to 
measure  a  secondary  reaction  which  is  really  equivalent  to  the 
primary.  From  the  terminology  of  photochemistry  the  term 
acceptor  has  been  used  to  designate  the  substance  acted  on  by 
the  product  of  the  primary  light  reaction.  Evidently  the  first 
requisite  in  testing  the  photochemical  equivalence  law  is  an 
acceptor  which  will  give  a  measurable  secondary  reaction  that  is 
equivalent  to  the  primary.  There  is  as  yet  no  theory  according 
to  which  the  action  of  a  given  acceptor  toward  a  given  primary 
product  can  be  predicted.  It  is  necessary  in  each  case  to  try  by 
experiment.  Early  failures  to  find  "suitable"  acceptors  for  the 
reactions  investigated  have  rather  retarded  progress,  but  as 
experience  is  accumulated  a  more  rapid  development  of  the 
subject  may  be  expected  in  the  future. 

55.    Experimental  Tests  of  the  Law  of  Photochemical  Equiv- 
alence. 

Warburg  -  was  one  of  the  first  to  undertake  experiments  in 
this  direction  and  was  followed  by  Bodenstein,  Lewis,  and  yet 
more  recently  by  Nernst,  his  co-workers,  and  others.  The  results 
of  the  earlier  work  were  summarized  in  1913  by  Bodenstein.^ 
The  following  Table  XV  gives  a  list  of  reactions  according  to 
Bodenstein  which  he  terms  "primary  light  reactions,"  in  which 
the  number  of  molecules  (M)  acted  on  in  the  primary  action  are 
either  equal  to  hv  or  exceed  it  by  small  multiples.  They  may 
be  regarded  as  cases  in  which  Einstein's  law  is  at  least  approxi- 
mately applicable. 

At  the  time  that  Bodenstein  made  the  classification  pre- 
sented in  Table  XV  he  was  of  the  opinion  that  the  primary  light 
reactions  are  the  result  of  direct  action  of  the  positively  charged 
ions  left  after  the  removal  of  an  electron  from  the  molecule.    As 

"  E,  Warburg,  Extended  series  of  papers  in  the  Sitzb.  Berlin  Akad.  Wisa. 
See  later  refs. 

»M.  Bodenstein,  Zeit.  pJiys.  Chem.  85,  333   (1913). 


134    THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELEC^ROi^S 


TABLE  XV 

Primary  Light  Reactions  According 

to  Bodenstein 

Reaction 

Authority  Absorption 

hv/M 

2HI  =  H2  +  I2 

B.*            weak 

? 

30,  =  203 

weak 
R.^    W.«      strong 

lfor203  (measd.) 

2NH3  =  N2  +  3H2 

RJ    W.«      strong 

4  (measd.) 

2H3O  =  2H,  +  0, 

Not  yet  measd.  without  photochemical  re 
combination. 

Anthracene— > 

1  to  0.7  (calcd.) 

dianthracene 

L.  &  W.°    medium 

3  (calcd.  by  B.) 

Decomp.  Levulose 

B.  &  G.^'^    medium 

1.4  (calcd.) 

C,H,NO,CHO^ 
CeH.NOCOOH 

W.  &K."    medium 
strong 

9  (calcd.) 

SX  =  Sfx 

W.^2         medium 

4  to  5  (calcd.) 

Quinine  oxidation  by- 
chromic  acid 

L.  &  F."    medium 

1.5  (calcd.) 

203  =  30,  (by  CI,) 

W.^*        medium 

1.7  (calcd.) 
0.8  (calcd.  by  B.) 

already  stated,  on  account  of  the  experimental  evidence  to  the 
.contrary  Bodenstein  ^^  was  forced  to  abandon  his  theory  and  to 
adopt  the  idea  of  Stark  ^^  that  the  primary  light  effect  consists 
in  loosening  the  valence  electrons  in  such  a  manner  as  to  render 
the  molecule  chemically  active.  This  change  of  theory  in  no 
way  affects  the  applicability  of  Bodenstein's  idea  of  primary 
light  reactions,  for  which  he  prescribes  the  following  character- 
istics:     (1)   Proportionality  between  the  quantity  of  chemical 

♦M.  Bodonstoin,  Zoit.  phys.  Chrm.  22,  23   (1897)  ;  fil,  447   (1007). 

•E,  Uegoner,  Ann.  d.  Phyaik  (4)  20,  1033   (190fi). 

«E.  Warburg,  Sitzh.  Akad.  Wise.  Perlln,  1912,  216. 

''  E.    Rogonor,   loc.   cit. 

«E.  Warburg,  Sitzh.  Alad.  ^Vi8s.  Berlin,  1911,  74G  ;  1912,  210. 

•R.  Luther  and  F.  Welgert,  Zcit.  phys.  Chcm.,  51,  297;  53;  385   (1905). 

"»  I).  Berthelot  and  II.  (;audec'bon,  Comp.  rend.  15(5,  707   (1913). 

"  F.  Wi'igcrt  and  L.  Kuninicrcr,  Ber.  4(),  1207   (1913). 

"A.  Wigand,  Zvit.  phys.  Vhem.,  11,  423  (1911). 

'»  R.  Luther  and  G.  S.  Forbes,  ihid.,  41,  1    (1902) 

'«F.  Weigert,  ihid.,  80,  103;  Zcit.  Elcktrochim.,  14,  591   (1908). 

"M.   Bodenstein,  Zcit.   Elckirochrm.,  22,  53-01    (1916). 

'•J.  Stark,  "Atonidynaniik,"  Leipzig.  1911.  Vol.  II.  p.  207. 


I 


PHOTOCHEMICAL  EQUIVALENCE  LAW  135 

reaction  and  the  absorbed  energy — with  a  corresponding  law 
for  reaction  velocity.  (2)  Absence  of  influence  of  foreign  sub- 
stances, and  (3)  absence  of  influence  of  temperature,  insofar  as 
they  do  not  influence  the  absorption  of  light.  (4)  One  molecule 
reacting  for  each  quantum  of  energy  absorbed  or  for  a  small 
number  of  the  latter. 

Under  secondary  light  reactions  Bodenstein  classed  those 
which  show  a  great  excess  over  or  deficiency  from  the  require- 
ments of  Einstein's  theory,  and  originally  assumed  that  the  excess 
action  is  due  to  the  multiplied  effect  of  the  free  wandering  elec- 
trons, as  already  explained  in  the  previous  chapter.  Upon  being 
forced  to  abandon  this  theory  for  the  same  reason  as  in  the  case 
of  the  primary  reactions,  Bodenstein  makes  the  assumption  that 
a  molecule  which  has  received  light  energy  (in  the  form  of 
loosened  valence  electrons)  does  not  lose  it  on  combining  with 
another  atom  or  molecule,  but  produces  a  compound  which  is 
capable  of  imparting  this  energy  to  certain  other  molecules  with 
which.it  comes  into  contact.  To  take  the  case  of  the  Hg — Clg 
reaction,  he  assumes  that  Clg  is  activated,  combines  with  ordi- 
nary H,  molecules  to  form  activated  HCl  which  can  impart  its 
activity  to  Clg  and  to  O2  (to  explain  dissipation  of  activity  by 
inhibitors),  but  not  to  neutral  gases  like  N2,  nor  to  Hg.  In  the 
following  section  will  be  presented  a  theory  by  Nernst  assuming 
atomization  of  CI2  as  the  primary  action.  Without  any  distinc- 
tion at  present  as  to  which  theory  has  greater  probability,  Boden- 
stein's  classification  of  the  secondary  light  reactions  has  the 
same  experimental  weight  as  it  originally  carried  and  is  there- 
fore given  in  the  following  Table  XVI. 

Luther  and  Goldberg  ^^  have  shown  that  in  all  the  photo- 
chlorinations  investigated  by  them  oxygen  acts  as  an  inhibitor, 
and  Bodenstein  makes  the  generalization  that  oxygen  inhibits  all 
the  secondary  photochemical  reactions  except  those  in  which  it 
takes  part  as  an  oxydizing  agent.  The  data  of  Bodenstein  and 
Dux  ^^  on  the  kinetics  of  the  photochemical  interaction  of  hydro- 
gen and  chlorine  served  as  a  basis  for  Bodenstein's  general  photo- 
chemical theory,  which  he  then  applied  to  other  photochemical 
reactions   with   the    following   modifications,   which    have   been 

"R.  Luther  and  E.  Goldberg,  Zeit.  phys.  Chcm.,  56,  43  (190G). 
'8M.  Bodenstein  and  W.  Dux,  ibid.,  85,  297-328   (1913). 


136  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

transformed  by  the  writer  into  terms  corresponding  to  his  later 
theory  instead  of  the  original  electronic  theory: 

(1)  It  is  not  always  the  substance  primarily  acted  on  by  light 
which  becomes  activated  for  the  secondary  reaction. 

(2)  The  velocity  of  the  secondary  effective  reaction  is  not 
always  excessively  large  compared  with  the  ineffective  reversion 
of  the  primarily  affected  substance  to  its  original  form. 

(3)  The  secondary  reaction  is  not  always  so  great  that  the 
primary  one  can  be  neglected  in  comparison,  as  in  the  case  of 
hydrogen  and  chlorine. 

(4)  Oxygen  inhibition  can  be  absent  in  case  oxygen  is  the 
substance  activated  in  the  secondary  reaction. 

(5)  Other  substances  can  act  as  inhibitors  and  either  take 
the  place  of  or  act  jointly  with  oxygen. 

In  Table  XVI  the  reactions  are  divided  by  Bodenstein  into 
three  classes:  I.  Those  in  which  oxygen  acts  as  inhibitor.  II. 
Those  in  which  oxygen  is  one  of  the  components  of  the  reaction 
and  does  not  inhibit.  III.  Those  in  which  the  primary  reaction 
can  not  be  neglected  in  comparison  with  the  secondary  reaction. 
lo  refers  to  the  light  absorption  by  A,  the  substance  primarily 
acted  on.  B  is  the  substance  activated  in  the  secondary  reaction. 
C  is  in  some  cases  a  third  reacting  substance,  dx/dt  indicates 
velocity  of  chemical  reaction  in  the  usual  differential  form. 

Recently  a  more  rigorous  test  of  Einstein's  photochemical 
equivalence  law  has  been  made  by  Nernst  ^^  and  Frl.  Pusch.^^ 
Nernst  emphasizes  the  necessity  of  paying  attention  to  the  pri- 
mary reaction  and  of  choosing  an  acceptor  which  neither  multi- 
plies nor  diminishes  the  products  of  the  primary  action,  but 
directly  transforms  them  into  the  equivalent  quantity  of  finally 
measured  product.  Frl.  Pusch  found  hydrogen  to  be  a  very 
unsuitable  acceptor  in  its  reaction  with  bromine,  the  amount  of 
action  falling  far  short  of  theory.  In  an  experiment  with  solar 
radiation  of  ten  hours'  duration,  the  quantity  of  bromine  com- 
bined was  0.02  g.,  where  2.3  grams  were  predicted  by  theory.  In 
experiments  with  a  "nitra"  (nitrogen  filled)  lamp  as  source  of 
light,  it  was  found  that  heptane,  hexane  and  toluene  all  combine 
with  bromine  at  a  rate  greater  than  theory,  but  hexahydroben- 

»»W.   Nernst,   Zeit.   Elektrochem.,  24,   33r>-G    (1918). 
«»Frl.  L.  Pusch,  ibid.,  24,  33G-9  (1918). 


PHOTOCHEMICAL  EQUIVALENCE  LAW 


137 


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.<   o      ^  o    o 

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o      o  o 


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o 


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138  THE  CHEMICAL  EFFECTS  OP  ALPHA  PARTICLES  AND  ELECTRONS 


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PHOTOCHEMICAL  EQUIVALENCE  LAW 


139 


zene  appeared  to  be  a  suitable  acceptor,  and  the  following  results 
were  obtained  by  Frl.  Pusch  for  several  different  exposures. 

TABLE  XVII 

Test  of  Photochemical  Equivalence  Law,  According  to  Frl.  Pusch 
Reaction:  Bromine  +  Hexahydrobenzene. 


Milligrams  of  Bromine  Combined 

Hours 

(Found) 

Calcd, 
(Einstein's  Law) 

8.25 
22.33 
20.25 
24.25 
24.00 

2.08 
5.95 
6.72 
5.66 
5.82 

1.82 
5.38 
5.10 
5.70 
5.51 

Since  the  appearance  of  Bodenstein's  classification,  Warburg 
has  tested  the  applicability  of  Einstein's  law  for  a  number  of 
additional  reactions.  For  the  decomposition  of  ozone  *^  he  finds 
that,  in  dilute  mixtures  where  the  total  pressure  is  one  atmos- 
phere, the  secondary  reaction  furnishes  a  new  confirmation  of  the 
law.  Photolysis  in  aqueous  solution  was  examined  in  the  case  of  de- 
composition of  nitrates  to  nitrites  *^  using  three  wave  lengths  sep- 
arately of  the  zinc  arc:  A,  =  0.214,  0.257,  and  0.274^,  respectively. 
The  reaction  was  faster  in  slightly  alkaline  than  in  acid  solution, 
was  independent  of  the  cation  and  of  the  degree  of  electrolytic 
dissociation.  Einstein's  law  was  not  followed,  the  reaction  being 
greater  for  short  than  for  long  wave  lengths.  The  effect  of  the 
solute  was  suggested  as  the  probable  cause.  The  conversion  of 
isomers  was  examined  for  the  reactions:  maleic -^  fumaric  acid 
and  the  reverse  action.*^  The  chemical  action  found  was  about 
4-13%  of  theory.  The  rate  for  maleic  -^  fumaric  increased  with 
increase  of  X  but  in  a  much  greater  ratio.  The  rate  of  the 
reverse  reaction  showed  the  opposite  effect,  thus  contraverting 


I 


*o  E.   Warburg,   Bcr.   Berlin  Akad.   Wiss. 
"E.   Warburg,  ihid.,   1918,   1228-4G. 
*2E.   Warburg,  iMd.,  1919,  960-74. 


1913,    644-59. 


140  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

the  Einstein  law.  The  effect  of  concentration  was  not  great. 
Further  tests  in  the  case  of  ammonia  decomposition  ^^  showed 
that  either  the  law  does  not  apply  or  that  much  ammonia  is 
reformed.  The  application  of  the  law  was  also  not  successful 
for  the  photolysis  of  HBr.** 

56.     Comparison  of  Photochemical  Equivalence  Law  and  Ionic- 
Chemical  Equivalence. 

Reference  to  Tables  VII,  XV  and  XVI  will  show  that  we  have 
the  same  kinds  of  variation  between  theory  and  experiment  both 
in  photochemical  and  in  a  ray  reactions.  In  both  we  have  a 
number  of  experimentally  investigated  reactions  in  which  agree- 
ment with  theory  is  as  good  as  could  be  expected  in  the  present 
status  of  experimentation.  We  also  have  in  both  cases  large 
departures  from  theory  in  either  direction.  On  account  of  these 
points  of  similarity  the  question  naturally  presents  itself  as  to 
whether  the  mechanism  of  reaction  is  not  identical  for  the  two 
different  forms  of  radiation. 

The  most  striking  case  of  greatly  excessive  action  among 
those  hitherto  investigated  by  a  radiation  has  been  shown  to  be 
that  of  hydrogen  and  chlorine  where  reaction  exceeds  theory  by 
something  like  10*.  Among  the  photochemical  reactions  we  find 
the  same  reaction  exceeding  theory  by  10®.  Bodenstein  {lac.  cit.) 
has  expressed  the  view  that  the  same  mechanism  must  control 
both  reactions.  It  would  be  of  great  interest  to  measure  the 
increasing  activity  of  hydrogen-chlorine  mixtures  with  different 
forms  of  radiation  to  see  whether  the  reactivity  increases  in  the 
same  proportion  for  all. 

To  explain  the  mechanism  by  which  such  large  excess  over 
theory  can  be  attained,  we  have  first  the  free  electron  theory  of 
Bodenstein,  which  had  to  be  abandoned  as  an  explanation  of 
photochemical  effects,  on  account  of  the  experimental  demonstra- 
tion of  the  absence  of  free  electrons;  but  which  may  still  hold 
for  the  a  ray  reactions,  unless  it  be  admitted  with  "Bodenstein, 
that  by  analogy  the  same  mechanism  must  hold  for  both.  Sec- 
ond, we  have  the  theory  of  loosened  electrons  of  Stark  for  which 
Bodenstein  has  made  the  assumption  that  the  light  energy  is 
retained  after  reaction  and  is  imparted  to  other  molecules,  ren- 

«E.  Wnrburjr,  lirr.  Berlin  A  had.  Wiss.,  1914,  872-85. 
"  E.  Warburg,  ibid.,  1916,  314-29. 


PHOTOCHEMICAL  EQUIVALENCE  LAW  141 

dering  them  active.  While  there  may  be  some  question  as  to  the 
probability  of  this  theory,  it  has  the  advantage  of  very  general 
applicability.  In  the  following  section  it  will  be  seen  that  Nernst 
has  proposed  an  atomistic  theory  to  account  for  the  hydrogen- 
chlorine  reaction,  which  is  based  on  purely  thermodynamic  con- 
siderations. While  it  has  great  probability  for  that  specific  reac- 
tion it  appears  to  be  inapplicable  directly  to  the  other  cases  of 
excessive  reaction.  W.  C.  M.  Lewis  has  proposed  a  radiation 
theory  which  is  discussed  in  §  58. 

The  cases  in  which  large  deficiencies  from  theory  are  observed 
have  all  been  explained  up  to  the  present  by  immediate  reversal 
of  the  primary  reaction.  In  this  sense,  an  acceptor  is  a  substance 
which  combines  with  the  products  of  the  primary  reaction  with- 
out allowing  them  to  recombine  among  themselves.  On  the 
other  hand,  the  additional  condition  must  be  imposed  upon  a 
''suitable"  acceptor,  from  the  standpoint  of  photochemical  equiv- 
alence, that  it  shall  not  by  any  other  process  multiply  the  output 
of  the  primary  reaction. 

57.    Mechanism  Proposed  by  Nernst  for  the  Hydrogen-Chlor- 
ine Photo-Reaction. 

Nernst  has  recently  applied  his  heat  theorem  *^  to  calculate 
the  following  heats  of  reaction: 

CI  +  CI  =  CI2  +  106,000  cal. 

H  +  H  =  H2  +  100,000  cal. 

CI  +  H2  =:  HCl  +  H  +  25,000  cal. 

H  +  CI2  =  HCl  +  CI  +  19,000  cal. 

and  H  +  CI  =  HCl  +  125,000  cal. 

From  the  known  absorption  of  chlorine  for  light  of  different 
wave  lengths  it  can  be  calculated  by  the  quantum  theory  within 
what  spectral  region  chlorine  can  be  dissociated  into  atoms. 
The  calculation  shows  that  this  can  be  accomplished  by  the 
wave  lengths  known  to  produce  chemical  combination  of  hydro- 
gen and  chlorine  and  the  assumption  of  the  existence  of  free  CI 
atoms  for  the  propagation  of  the  photo-reaction  is  therefore 
justified.  The  heat  of  reaction  shows  that  the  combination  of 
a  CI  atom  with  a  Hg  molecule  and  the  subsequent  splitting  of 

«W.  Nernst,  Sitzh.  Berlin  Akad.  Wiss.,  1911,  Go-90 ;  also  "Gruudlagen  d. 
neuen  Warmesatzes"   (1918),  p.  133. 


142  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

this  unstable  product  to  HCl  and  a  free  H  atom  take  place  with 
a  large  heat  evolution,  and  therefore  in  the  direction  of  sponta- 
neous reaction  according  to  the  chemical  free  energy.  Moreover, 
when  a  free  H  atom  (just  produced  by  the  foregoing  reaction) 
unites  with  a  CI2  molecule  we  again  have  a  reaction  of  the  same 
nature.  The  CI  atom  liberated  by  the  latter  reaction  brings  us 
back  to  the  original  system,  and  a  cycle  has  been  completed 
which  may  repeat  itself  indefinitely,  except  for  the  cross  reaction 
of  H  and  CI  atoms,  and  for  the  inhibitive  effect  of  oxygen,  which 
is  assumed  to  remove  the  free  CI  atoms  from  the  field  of  action. 
By  this  purely  thermodynamic  method  Nernst  explains  the  multi- 
plied secondary  reaction  in  a  mixture  of  Hg  and  CI2,  which 
accounts  for  the  large  departure  from  Einstein's  law  through  the 
action  of  free  atoms.  In  further  support  of  the  theory,  Nernst 
calculates  that  a  similar  continuous  cycle  in  the  case  of  hydrogen 
and  bromine  is  impossible,  because  one  of  the  steps,  Br  +  Hg, 
would  not  proceed  spontaneously  on  account  of  a  negative  heat 
of  reaction,  —15,000  cals.  And  of  course  it  is  well  known  that  a 
mixture  of  H2  +  Brg  is  not  light  sensitive  at  ordinary  tempera- 
ture. The  further  application  of  this  or  similar  mechanisms  to 
explain  other  cases  of  excessive  action  has  not  been  attempted, 
but  it  is  not  without  interest  to  note  that  in  the  only  other  two 
cases  where  the  M/N  value  is  as  high  as  10^  (Table  XVI),  we 
have  halide  and  hydrogen  present  in  the  system. 

58.     General  Radiation  Theory  of  Chemical  Action. 

In  an  extended  series  of  investigations,  Lewis  and  his  co- 
workers ^®  have  proposed  a  radiation  theory  of  chemical  action 
which  appears  to  be  of  fundamental  importance  in  chemical 
kinetics,  and  which  also  has  afforded  additional  confirmation  of 
the  applicability  of  Einstein's  law.  A  general  review  of  Lewis's 
theory  and  his  deductions  from  it  is  pertinent  to  the  subject  of 
the  present  chapter. 

It  has  long  been  recognized  that  the  usual  positive  tempera- 
ture coefficient  of  chemical  reaction,  which  is  of  the  order  of  a 

*«A.  Lamble  and  W.  C.  McC.  Lewis,  Journ.  CJtcm.  Soc.  Lond.,  105ji ,  2330-42 
(1914);  107,,  233-48  (1915).  R.  H.  Callow  and  Lewis,  ihid.,  109,-,  55-07 
(1916).  R.  O.  Griffith  and  Lewis,  ihid.,  109,,  67-83  (1910).  Lewis,  ihid.,  109„, 
796-815  (1916).  R.  O.  Griffith,  A.  Lamble  and  Lewis,  ihid..  Ill,,  389-95  (1917). 
Lewis,  ihid.,  11,,  457-09;  111,,,  1086-1102  (1917);  113,  471-92  (1918);  115, 
182-93   (1919)  ;  Rep.  Brit.  Assoc.   (1915),  p.  394. 


PHOTOCHEMICAL  EQUIVALENCE  LAW  143 

2  to  3  fold  increase  for  an  interval  of  10*^0.,  can  not  be  explained 
by  the  mere  increase  of  kinetic  energy  of  the  reacting  molecules. 
It  has  also  been  rather  generally  assumed  that  the  molecules, 
before  they  react,  must  in  some  way  be  activated,  and  that  this 
process  is  the  one  influenced  by  increase  of  temperature. 

In  1889  Arrhenius  *^  deduced  a  relation  based  on  the  assump- 
tion of  a  mass  action  equilibrium  between  active  and  inactive 
molecules,  of  the  form:  d  log  k/d  T  =  A/T^,  in  which  k  is  the 
velocity  constant  of  chemical  action,  T  is  the  absolute  tempera- 
ture, and  A  is  one  half  of  the  energy  required  to  change  1  Mol 
of  inactive  to  active  modification.  This  formula  has  since  been 
shown  to  be  of  very  general  experimental  applicability,  although 
its  theoretical  basis  is  no  longer  tenable  for  the  following  reasons. 
The  conception  of  Arrhenius,  or  indeed  any  other  theory  that 
attempts  to  explain  velocity  of  reaction  as  controlled  by  tempera- 
ture, leads  directly  to  the  consideration  of  the  effect  of  catalysts, 
and  that  of  Arrhenius  to  the  prediction  that  the  temperature 
coefficient  should  be  diminished  in  a  homogeneous  system  by 
the  increase  of  the  concentration  of  the  catalyst.  This  predic- 
tion has  not  been  confirmed  by  later  work,  including  that  oif 
Lewis,  who  found  that  the  temperature  coefficient  of  the  rate  of 
hydrolysis  of  methyl  acetate  is  independent  of  the  concentration 
of  acid.  Recent  work  of  Taylor  *^  in  the  laboratory  of  Arrhenius 
has  cast  further  doubt  upon  the  existence  of  "active"  molecules 
(in  the  sense  of  Arrhenius). 

In  1914  Marcelin*^  treated  the  effect  of  temperature  on 
velocity  of  reaction  as  a  purely  physical  one  dependent  on 
the  increase  of  the  internal  energy  of  the  reacting  molecule, 
and  arrived  at  a  formulation  similar  to  that  of  Arrhenius: 
d  logk/dT  =  E/RT^,  in  which  E  is  defined  as  the  critical  energy 
that  must  be  absorbed  by  the  molecule  to  render  it  active.  Lewis 
suggests  that  E  be  called  the  critical  increment  to  emphasize 
that  it  is  the  excess  energy  that  must  be  absorbed  by  the  acti- 
vated molecules  above  the  average  energy  possessed  by  all 
molecules. 

Rice^°  has  developed  in  more  exact  mathematical  form 
the  same  equation:  d  logk/dT  ==  (V «-¥„,+ 1/2 (RT)  )/KT\  in 

1*^  Sv.  Arrhenius,  Zeit.  phys.   Chem.,  4,  226-48    (1889). 
"  H.  S.  Taylor,  Mcdd.  Vetemkcipsakad.  NoJ)cUnst.  2,  No.  34   (1912). 
*»R.  Marcelin,  Comp.  rend.  158,  161   (1914). 
•oj.  Rice,  Rep.  Brit.  Assoc.   (1915),  p.  397. 


144'  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 


which  Y^  is  the  mean  value  of  the  potential  energy  of  the  mole- 
cules and  V^  is  the  critical  value  which  must  be  attained  before 
chemical  reaction  ensues.  Rice's  formulation  was  used  by  Lewis 
in  the  development  of  the  radiation  theory  applied  to  catalysis 
and  later  to  chemical  action  in  general.  The  application  to 
catalysis  has  been  adopted  and  explained  by  Rideal  and  Tay- 
lor." 

Lewis  {loc.  cit.)  advances  the  hypothesis  that  the  energy 
increment  is  imparted  to  the  molecule  by  means  of  infra- 
red radiation,  and  that  the  Einstein  Law  is  applicable  to 
the  energy  absorption.  The  energy  increment  can  be  calcu- 
lated directly  from  the  temperature  coefficient,  as  follows: 
logkgs/kgg  =  E/R(  1/298—  1/308).  For  the  hydrolysis  of  methyl 
acetate  the  coefficient  for  a  10°  interval  at  ordinary  temperature 
is  about  2.5,  from  which  E  is  calculated  to  be  16,800  cals.  per 
g.mol.,  or  1.03x  lO'^^ergs  per  single  molecule.  From  Einstein's 
law  Lewis  calculates  that  for  the  infra-red  radiation  of  X  :=  7.5^ 
for  methyl  acetate  (Coblentz  ^^),  hv  should  be  0.262  x  10"^^  gj-gg^ 
or  that  4hv  should  suffice  to  furnish  the  required  energy  E.  Con- 
versely Lewis  has  calculated  from  the  velocity  of  the  H  ion 
(electrolytic)  and  its  probable  free  path  that  it  would  have  a 
vibration  frequency  falling  in  the  region  of  the  known  absorption. 

Lewis's  suggestion  that  catalysis  is  in  general  a  radiation 
phenomenon  is  supported  by  the  theory  of  Trautz  °^  and  later  by 
that  of  Kriiger,^*  who  showed  that  the  processes  of  solution, 
solution  pressure,  solubility  and  electrolytic  dissociation  can  be 
explained  on  the  basis  of  radiation,  which  in  turn  can  be  related 
to  the  dielectric  constant  of  the  solvent.  According  to  Lewis's 
conception  the  function  of  a  catalyst  is  to  absorb  the  infra-red 
radiation  of  the  chemical  system  and  to  transfer  the  energy  to 
the  reacting  molecule.  In  this  sense  catalysis  is  evidently  but  a 
special  case  of  chemical  reaction,  where  the  absorption  is  accom- 
plished by  the  catalyst  instead  of  by  the  reacting  substance 
itself.  All  reactions  taking  place  in  a  solvent  must  be  regarded 
as  catalytic. 

A  still  further  step  has  been  taken  by  Lewis   (loc.  cit.)  in 

»'E.  Rldeal  and  H.  S.  Taylor,  "Catalysis  in  Theory  and  Practice"  (1919), 
p.  58  et  acq. 

w  W.   W,  Coblentz,  Pub.   Carnegie  Inst.,   Washington,  1905,  35. 
MM.  Trautz,  Zcit.  xriss.  Phot.,  4,  IGO   (1906). 
"H.  KrUger,  Zcit.  ElcJctrochcm.,  17,  453   (1911). 


i 


I 


PHOTOCHEMICAL  EQUIVALENCE  LAW  '  145 

applying  his  theory  to  uncatalyzed  homogeneous  gas  reactions. 
Strictly,  Einstein's  law  is  applicable  only  when  n  (index  of 
refraction)  =  1,  which  is  true  only  in  the  case  of  gases.  Lewis's 
theory  applies  to  bimolecular  homogeneous  reactions  of  the  type 
2HI  =  H2  + 12,  with  a  fairly  good  agreement  with  the  Einstein 
law.  Heterogeneous  (contact)  catalysis  can  also  be  explained 
by  Lewis's  theory  on  the  basis  of  Langmuir's  ^^  hypothesis  regard- 
ing the  spacial  distribution  of  molecules  and  atoms  at  the  inter- 
face between  two  phases.  The  energy  increment  is  lowered  at 
the  contact  surface,  which  is  in  agreement  with  the  lower  tem- 
perature coefficients  of  heterogeneous  chemical  reactions. 

Lewis  ^^  has  recently  pointed  out  the  anomalous  case  of  mono- 
molecular  homogeneous  gas  reactions,  which  differ  from  the  bimo- 
lecular reactions  in  the  pronounced  failure  of  Einstein's  law. 
The  value  of  the  velocity  constant  for  the  rate  of  dissociation  of 
PH3  observed  by  Trautz  and  Bhandarkar  ^^  is  about  10^  greater 
than  calculated  by  Lewis  from  Einstein's  law  on  the  assump- 
tion of  continuous  absorption.  For  discontinuous  absorption  the 
discrepancy  becomes  still  greater.  In  view  of  the  approximate 
agreement  for  bimolecular,  reactions  this  great  departure  for 
monomolecular  reactions  is  all  the  more  notal^e. 

Baly  ^^  has  applied  the  quantum  theory  to  spectroscopic  and 
fluorescent  phenomena.  According  to  his  theory  a  molecule  may 
absorb  radiation  by  quanta  of  a  given  frequency  and  radiate  a 
larger  number  of  quanta  as  a  result  of  chemical  action  at  a  lower 
frequency.  Chemical  action,  excessive  from  the  standpoint  of . 
Einstein's  law,  can  then  be  explained  by  re-absorption  of-  this 
internal  radiation,  a  process  that  will  result  in  further  chemical , 
action  that  may  be  multiplied  to  very  large  quantities  from  one 
quantum  primarily  absorbed.  Baly  proposes  this  explanation  for 
the  large  excess  observed  in  the  thermal  decomposition  of  phos- 
phine  and  also  for  the  photochemical  decomposition  of  hydrogen 
peroxide  and  hydrolysis  of  acetone.^^  , 

It  should  be  mentioned  that  Perrin  ^°  independently  arrived , 

"I.  Langmuir,  Journ.  Amer.  Chem.  8oc.  38,  2221  (1916). 

^W.  C.  McC.  Lewis,  Phil.  Mag.    (G)    39,  2G-31    (1920).  •  , 

57  M.  Trautz  and  D.  S.  Bhandarkar,  Zeit.  anorg.  Chem.  106,  95   (1919) 

WE.  C.  C.  Baly,  Phil.  Mag.   (6)   40,  1-15;  15-31    (1920). 

6«V.  Henri  and  R.  Wunnser,  Com/),  rend.  15(5,  1012   (1913). 

*»J.  Perrin,  Ann.  de  Physique   (9)    11,  5-108    (1919). 


146  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

at  a  general  radiation  theory  of  chemical  action  which  is  very 
similar  to  that  of  Lewis. 

The  type  of  radiation  that  is  involved  in  Lewis's  theory  is 
very  different  from  the  corpuscular  forms  that  are  treated  in 
this  monograph  and  also  from  those  of  the  usual  photochemical 
effects.  In  the  infra-red  absorption  the  energy  increment  is  not 
a  large  fraction  of  the  chemical  energy  of  the  reaction,  whereas, 
in  the  case  of  the  corpuscular  and  photochemical  radiation  effects, 
the  energy  applied  is  usually  largely  in  excess  of  the  net  chemical 
energy  involved  in  the  reaction. 

With  reference  to  the  emission  of  infra-red  radiation  by  chem- 
ical reactions,  the  recent  work  of  David  ^^  should  be  cited,  who 
has  shown  that  the  explosive  combination  of  oxygen  with  coal 
gas  and  with  hydrogen  results  in  the  emission  of  radiation  of 
wave  lengths  X  =  2.8^i  and  4.4pi.  Although  the  temperature  of 
reaction  in  the  experiments  of  David  is  estimated  at  1200°,  he 
is  of  the  opinion  that  the  radiation  is  due  to  the  chemical  action 
and  not  to  temperature  effect. 

Further  contributions  to  the  radiation  theory  of  chemical  ac- 
tion have  been  very  recently  made  by  Langmuir,^^  Rideal,"^ 
Lindemann  ^*  and  Tolman.®^  Langmuir  makes  a  fundamental  in- 
quiry into  the  basis  of  the  radiation  hypothesis  of  chemical  ac- 
tion and  concludes  (1)  that  it  has  not  been  satisfactorily  demon- 
strated that  the  radiation  emitted  by  a  chemical  action,  as  cal-. 
culated  from  the  temperature  coefficient,  falls  in  the  absorption 
region  of  the  system;  (2)  that  the  total  radiation  is  not  nearly 
sufficient  to  account  for  chemical  activation  and  that  the  radia- 
tion hypothesis  is  untenable.  Langmuir  believes  that  the  in- 
ternal energy  of  the  molecule  is  the  ultimate  source  of  its  acti- 
vation. Lindeman  points  out  (as  does  Langmuir  also)  that  ac- 
cording to  the  radiation  hypothesis  many  reactions  should  be 
photo-sensitive  which  fail  to  exhibit  this  effect;  Tolman  adopts 
the  view  of  Lewis,  Perrin  and  Marcelin  that  the  similar  form 
of  the  Arrhenius  equation  and  the  Wien  radiation  law  justifies 
the  radiation  hypothesis  of  chemical  action.     Tolman  employs 

"W.  T.  David,  Phil.  Mag.  (6)  39,  66-83;  84-95  (1920).  Trans.  Roy.  Soc. 
Lond.,  211,  375;  Proc,  85,  537   (1911). 

~I.   Lnngmuir,  J.  Am.   Chem.   Soc,  42,  2190-2205    (1920). 
"Eric  K.  Rideal,  Phil.  Mag.   (0)   40,  461-6    (1920). 
•*F.  A.  Lindemann,  ihid.   (6)    40,  671-4    (1920). 
»P,  C.  Tolman,  J.  A^n.  Ch^m.  Soc,  42,  2506-?8  (1980), 


PHOTOCHEMICAL  EQUIVALENCE  LAW  147 

the  principles  of  statistical  mechanics  to  develop  the  Rice- 
Marcelin  equation  and  also  makes  many  other  applications  im- 
portant to  chemical  kinetics.  Rideal  employs  a  formula  of 
Langmuir  and  Dushman  to  develop  the  equation  for  velocity  of 

dn  -hy 

reaction:  -—  =  y.e    kt  ,  in  which  n  is  the  number  of  molecules 
dt 

reacting  per  second,  v  is  the  frequency,  and  all  other  symbols 
having  the  usual  meaning.  Applying  this  to  the  decomposition 
of  PHg,  the  velocity  constant  is  calculated  to  be  3.5  x  10"^,  the 
same  order  of  magnitude  as  that  observed  10.2  x  10"^. 

Daniels  and  Johnston  ^^  have  recently  investigated  the  ther- 
mal and  photochemical  decomposition  of  gaseous  NgOg.  The 
thermal  action  is  monomolecular  and  proceeds  at  room  tempera- 
ture. The  critical  increment  as  calculated  from  the  temperature 
of  the  velocity  of  decomposition  is  independent  of  the  tempera- 
ture. Its  value,  24,700  calories,  indicates  according  to  the  radi- 
ation theory  that  the  reaction  should  be  catalyzed  by  light  of 
wave  length  =  1.16^1.  Photochemical  investigation  failed  to  con- 
firm this  prediction.  Light  in  the  region  400— 460np,  does  accel- 
erate the  decomposition,  but  only  in  the  presence  of  NOg.  The 
interesting  theory  is  proposed  that  the  catalytic  effect  of  NO2 
is  due  to  its  absorption  of  blue  light  over  a  wide  spectral  range 
and  that  through  fluorescence,  radiation  is  emitted  in  the  infra- 
red region  where  its  absorption  lines  coincide  with  those  of  NgOg, 
causing  decomposition  of  the  latter.  Experimental  evidence  of 
the  actual  fluorescence  of  the  NO2  and  of  the  decomposition  of 
N2O5  by  radiation  in  the  infra-red  region  remains  to  be  obtained. 

80  F.  Daniels  and  E.  H.  Johnston,  J.  Am.  Chem.  Soc.,  43,  53-81  (1921). 


Chapter  11.  : 

Positive  Eays  and  Eecoil  Atoms. 

59.'   General  Nature  of  Positive  Rays. 

In  1886  it  was  observed  by  Goldstein^  that  if  he  used  a  per- 
forated cathode  in  examining  electrical  discharge  through  air  at 
low  pressure,  luminous  beams  of  rays  could  be  seen  traversing  the 
space  back  of  the  cathode,  t.  e.  on  the  side  away  from  the  anode, 
which  apparently  came  through  the  channels  in  the  cathode. 
On  account  of  their  mode  of  formation  or  demonstration  Gold- 
stein called  them  "canal"  rays.  It  has  since  been  shown  that 
they  are  the  positively  charged  gaseous  ions  which,  at  low  gas 
pressure,  attain  sufficient  velocity  toward  the  cathode  or  nega- 
tive pole  to  carry  them  through  the  perforations  into  the  space 
behind,  where  they  can  be  observed  by  means  of  phosphorescent 
screens  or  by  their  action  on  the  photographic  plate. 

In  1898  Wien  ^  demonstrated  the  deflection  of  the  canal  rays 
by  a  strong  magnetic  field.  Since  this  time  J.  J.  Thomson  ^  has 
conducted  a  series  of  investigations  which  have  resulted  in  dis- 
coveries of  the  greatest  importance  both  to  physics  and  chemis- 
try. It  has  been  recommended  by  Thomson*  that  the  more 
correctly  descriptive  term,  positive  rays  of  electricity,  be  used 
instead  of  canal  rays. 

Thomson  *  has  elaborated  a  technique  to  determine  by  means 
of  deflection  in  a  combined  magnetic  and  electrostatic  field  the 
e/m  value  of  each  type  of  positive  ray.  The  effects  due  to  the 
superposition  of  the  electric  and  magnetic  fields  simultaneously 
applied  have  been  analyzed  by  Thomson  in  the  following  way: 
If  the  forces  are  applied  parallel  to  the  axis  of  z,  the  y  and  z 
defiections  of  the  particle   are  given   by   the   two  equations: 

IE.  Goldstein,  8Uzb.  Aknd.  Wias.,  Berlin,  1886,  p.  G91 ;  Wied.  Ann.,  04,  38 
(1898). 

«W.  Wien,  Verh.  deut.  phya.  Qea.,  17,  ..   (1898). 

•J.  J.  Thomson,  Phil.  Mag.   (G)   21,  225-49   (1911)  ;  24,  209-53   (1912). 

*J.  J.  Thomson,  "Rays  of  Positive  Electricity"   (1913). 

148 


POSITIVE  RAYS  AND  RECOIL  ATOMS  149 

y  =  e/mv.A  and  z  =  e/mv-.B,  in  which  A  and  B  depend  only  on 
the  strengths  of  the  magnetic  and  electrical  fields,  respectively, 
and  the  distance  of  the  projection  from  the  point  of  deflection, 
and  can  be  made  constant  for  a  given  experiment.  In  the  absence 
of  any  field  all  positive  rays  would  pass  through  the  narrow 
aperture  in  the  cathode  and  be  recorded  on  the  photographic 
plate  at  the  same  spot  x  =  1,  the  distance  of  the  plate  from  the 
source.  Under  the  selective  action  of  the  two  forces  the  particles 
are  sorted  out  and  no  two  strike  the  plate  at  the  same  spot  unless 
they  are  moving  with  the  same  velocity  and  have  the  same  e/m 
value.  By  combining  the  two  equations  just  given  above  we 
have:  v  =  y/z.B/A  and  e/m  =  yVz-B/A^.  The  first  shows  that 
y/z  is  constant  for  all  particles  moving  with  a  given  velocity  v, 
no  matter  what  their  charge  or  mass  is,  and,  therefore,  will  all 
lie  on  the  plate  in  a  straight  line  passing  through  the  undeflected 
position  of  the  particles.  The  second  equation  shows  that  for 
the  same  kind  of  particles,  y  Vz  is  constant  no  matter  what  their 
velocity;  hence,  all  particles  of  the  same  kind  will  trace  on  the 
plate  a  parabola  with  its  vertex  at  the  undeflected  position  of 
the  particles.  Each  parabola  will  represent  a  different  kind  of 
particle.  This  principle  has  been  used  by  Thomson  and  his 
co-workers  as  a  method  of  positive  ray  analysis,  which  will  be 
described  in  the  following  section. 

60.    Thomson's  Method  of  Positive  Ray  Analysis. 

Thomson's  experimental  method  has  been  very  fully  described 
in  his  ''Rays  of  Positive  Electricity."  The  latest  modiflcation 
of  the  apparatus,  termed  mass-spectrograph,  has  recently  been 
thoroughly  described  by  Aston.^  Only  a  few  of  the  most 
important  experimental  features  will  be  mentioned  here  before 
passing  on  to  a  consideration  of  the  results.  A  very  large 
spherical  bulb  (20  cms.  diameter)  is  employed  for  the  discharge 
between  the  anode  and  cathode  in  order  to  favor  the  passage  of 
current  at  very  low  pressure.  A  silica  anticathode  is  used  which 
has  the  advantages  of  infusibility  and  of  giving  no  disturbing 
X  radiation.  The  two  cathode  slits  which  give  direction  to  the 
beam  of  positive  rays  are  of  aluminium  2  mm.  long  and  0.05  mm. 
wide.    The  space  between  the  slits  10  cms.  long  is  kept  at  the 

•F.  W.  Aston,  Phil.  Mag.   (6)   39,  611-2G  (1920). 


150  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRON^ 

highest  possible  vacuum  by  a  side  tube  of  charcoal  immersed  in 
liquid  air.  Beyond  the  slit  system  is  the  electrical  field,  200  to 
500  volts,  between  two  flat  brass  surfaces  2.8  mms.  apart  and  5 
cms.  long.  Beyond  the  electrical  field  is  the  magnetic  field  in 
which  the  rays  pass  between  the  pole  pieces  of  a  large  DuBois 
magnet  of  2500  turns,  the  faces  of  which  are  circular,  8  cms.  in 
diameter  and  3  mms.  apart.  The  current  for  the  magnet  is  pro- 
vided by  a  set  of  large  accumulators.  A  current  of  0.2  ampere 
jiist  brings  the  H  lines  onto  the  plate,  while  5  amperes  just 
bring  the  singly  charged  Hg  lines  into  view.  The  camera  cham- 
ber is  provided  with  a  special  plate  holder  arranged  so  that  the 
plate  can  be  shifted  for  several  different  exposures  without  open- 
ing the  chamber.  Exposures  from  2iO  seconds  for  the  H  lines,  up 
to  30  minutes  or  more  are  required.  The  discharge  in  the  large 
chamber  is  maintained  by  means  of  a  large  induction  coil  with 
a  Hg  coal-gas  break.  100  to  150  watts  are  passed  through  the 
primary  circuit,  and  the  bulb  itself  takes  0.5  to  1.0  milliampere 
at  20,000  to  50,000  volts. 

The  measurement  of  the  photographic  plates  to  determine 
the  mass  of  the  positive  rays  is  made  by  means  of  a  special 
comparator  capable  of  measuring  in  two  directions.  Theoreti- 
cally an  unknown  mass  may  be  determined  from  one  known  on 
the  same  plate,  but  practically,  greater  accuracy  is  obtained  by 
bracketing  the  unknown  with  several  known  lines  just  as  in 
ordinary  spectral  line  measurements. 

The  photographic  method  does  not  yield  an  insight  into  the 
relative  quantities  of  the  different  rays.  This  has  been  accom- 
plished by  Thomson  by  substituting  for  the  camera  a  Wilson 
tilting  electroscope  to  determine  the  total  charge  under  the 
following  conditions.  The  condenser  into  which  the  positive  rays 
are  received  is  provided  with  a  parabolic  slit,  which  in  principle 
might  be  moved  to  any  part  of  the  field  to  admit  rays  of  a  given 
mass  for  quantitative  measurement  by  means  of  their  charge. 
Instead  of  actually  moving  the  slit  it  is  made  stationary  and  the 
rays  of  different  masses  are  successively  brought  to  it  by  varying 
the  magnetic  field  strength. 

Thomson  has  determined  the  various  types  of  ions  which  are 
produced  in  different  gases.  The  variety  of  ions  for  a  given  sub- 
stance is  very  large  compared  with  electrolytic  ions.  Certain 
characteristics  have  been  pointed  out  by  Thomson  which  are 


I 


POSITIVE  RAYS  AND  RECOIL  ATOMS  151 

very  useful  in  determining  what  mass  is  represented  by  a  given 
m/e  value.  Multiple  charge  is  found  only  in  the  case  of  atoms." 
Molecules  either  of  elements  or  of  compounds  have  not  been  found 
to  be  multiply  charged  with  either  sign.^  The  heavy  atoms  show 
multiple  charge  to  a  higher  degree  than  do  the  lower  ones. 
There  is  no  apparent  relation  between  the  chemical  properties 
of  the  element,  such  as  valence  and  the  number  of  charges. 
Mercury  can  have  as  many  as  eight  charges,  oxygen,  nitrogen, 
and  neon  two;  hydrogen  never  more  than  one,  which  is  the  only 
element  examined  for  which  no  multiple  charges  have  ever  been 
found. 

61.    Isotopes  of  Neon. 

As  early  as  1912  Thomson  obtained  some  evidence  by  the 
positive  ray  method  of  the  existence  of  particles  of  mass  22  in 
neon  gas.  Aston  ^  has  recently  determined  the  mass  spectra  of 
neon  by  the  positive  ray  method  with  an  accuracy  of  1  in  1000 
parts.  The  measurements  show  conclusively  that  neon  consists 
of  two  isotopes  of  masses  20  and  22,  in  the  proportion  of  about 
nine  of  the  former  to  one  of  the  latter,  which  accounts  for  the 
observed  atomic  weight  20.2.  There  is  also  a  faint  indication  of 
a  third  isotype  of  mass  21  in  a  proportion  estimated  as  less  than 
1%.  If  this  third  isotope  proves  to  have  real  existence  it  will 
constitute  a  very  interesting  continuation  of  the  system  of  triads 
like  iron,  nickel  and  cobalt,  which  was  predicted  in  1895  by 
Reynolds,®  purely  from  analogy  with  the  three  other  well  known 
groups  of  triads. 

Attempts  have  been  made  by  Lindemann  and  Aston®  to 
separate  the  two  modifications  of  neon  by  fractional  distillation 
and  by  fractional  diffusion  through  pipe-clay.  Later  Linde- 
mann ^°  discussed  the  theory  of  the  separation  and  decided  that 
the  negative  result  obtained  was  the  one  to  have  been  expected 
under  the  experimental  conditions,  in  the  case  of  fractional  dis- 
tillation. The  fractional  diffusion  resulted  in  an  apparent  differ- 
ence of  density   of  about  0.7%,  while   an   automatic   method 

'Except  in  case  of  fluorides  of  boron  and  silicon.  (F.  W.  Aston,  PMl. 
Mag.  (6)  40,  630  (1920). 

'F.  W.  Aston,  Phil.  Mag.   (6)   39,  449-55   (1920). 

« E.  Reynolds,  Nature,  Marcli  21,  1895. 

•F.  A.  Lindemann  and  F.   W.  Aston^  PMl.  Mag.    (6)    37,   523-35    (1919). 

10  F.  A.  Lindemann,  iMd.,  38,  173-81  T1919). 


152  THE  CHEMICAL  EPFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

started  in  1914  gave  a  difference  of  only  0.3%.  It  can  therefore 
be  said  at  the  present  time  that  the  diffusion  method  in  the  case 
of  neon  has  given  positive  results  but  the  differences  are  too  small 
to  be  conclusive. 

62.    Discovery  of  Other  New  Isotopes  by  Aston. 

Still  more  recently  Aston  ^^  has  extended  the  search  for  iso- 
topes by  the  positive  ray  method  to  other  elements.  His  investi- 
gations have  yielded  results  which,  while  absolutely  astounding 
to  chemists  in  one  sense,  must  be  regarded  as  having  been  fore- 
shadowed by  Front's  ^^  hypothesis  more  than  one  hundred  years 
ago.  At  the  time  of  writing  (Oct.,  1920)  eighteen  elements  have 
been  examined  by  Aston  with  the  following  results,  H,  He,  C, 
N,  O,  F,  F,  and  As  give  a  pure  mass  spectrum  indicating  but 
one  isotope,  as  would  be  expected  from  their  whole  number 
atomic  weights.  The  results  for  the  other  elements  can  be  seen 
in  the  following  Table  XVIII.  The  case  of  bromine  is  of  par- 
ticular interest.  Although  its  atomic  weight  (79.92)  is  quite  close 
to  80,  there  appears  to  be  no  isotope  of  the  mass  80  at  all,  but 
two  isotopes  in  almost  equal  quantities  of  79  and  81. 

As  the  atomic  weights  of  the  elements  increase  it  becomes 
more  difficult  to  get  a  definite  resolution  of  isotopes  of  masses 
differing  by  one  or  two  units,  since  the  percentage  difference  is 
small.  The  whole  number  rule  on  the  basis  of  O  =  16  has  not 
hitherto  been  departed  from  in  any  case  except  hydrogen.  This 
may  be  related  to  the  absence  of  electrons  in  the  hydrogen 
nucleus.  At  any  rate  it  seems  very  well  established  that  the 
departures  of  the  ordinary  atomic  weights  from  unity  is  to  be 
accounted  for  by  a  mixture  of  whole  number  isotopes.  The 
occurrence  of  isotopes  appears  to  become  more  common  among 
the  elements  of  higher  atomic  weight;  apparently,  there  are  more 
complex  than  simple  elements.  The  influence  this  is  likely  to 
have  in  practical  and  theoretical  chemistry  has  been  expressed 
by  Aston  {lac.  cit.)  as  follows.  "The  very  large  number  of  dif- 
ferent molecules  possible  when  mixed  elements  unite  to  form 
compounds  would  appear  to  make  their  theoretical  chemistry 

«  F.  W.  Aston,  Nature,  105  ;  p.  8 ;  p.  54G ;  pp.  617-19  (1920).  Phil.  Mag.  (6) 
89,  611-25;  40,  628-34   (1920). 

"W.  Ostwald,  Grundri88  d.  allgemcinen  Chemie  (1899),  p.  41.  S.  L,  Blge- 
low,   "Theoretical  and  Pliysical  Chemistry"    (1912),  p.  87. 


POSITIVE  RAYS  AND  RECOIL  ATOMS 

TABLE  XVIII       • 


153 


Isotopes  ^^  of  the  Ordinary  Elements  According  to  Positive  Ray 
Analysis  by  Aston'^^ 


Element 


H 
He 
B 
C 

N 

0 

F 

Ne 

Si 

P 

S 

CI 

A 

As 

Br 

Kr 

X 

Hg 


Atomic 

Atomic 

Number 

Weight 

1 

1.008 

2 

3.99 

5 

10.9 

6 

12.00 

7 

14.01 

8 

16.00 

9 

19.00 

10 

20.2 

14 

28.3 

15 

31.04 

16 

32.06 

17 

35.46 

18 

39.88 

33 

74.96 

35 

79.92 

36 

82.92 

54 

130.2 

80 

200.6 

Minimum 

No.  of 

isotopes 


1 

1 

2 

1 

1 

1 

1 

2 

2 

1 

1 

2 
(2) 

1 

2 

6 

5 
(6) 


Mass  in  the  Order  of 
Intensity 


1.008 

4 

11,10 

12 

14 

16 

19 

20,22,(21) 

28, 29,  (30) 

31 

32 

35,  37, (39) 

40,  (36) 

75 

79,  81 

84,  86,  82,  83,  80,  78 

(128, 131, 130, 133, 135) 

(197-200),  202, 204 


almost  hopelessly  complicated,  but  if,  as  seems  likely,  the  sepa- 
ration of  isotopes  on  any  reasonable  scale  is  to  all  intents 
impossible,  their  practical  chemistry  will  not  be  affected,  while 
the  whole  number  rule  introduces  a  very  desirable  simplification 
into  the  theoretical  aspects  of  mass." 

The  attempts  of  Lindemann  and  Aston  to  separate  the  two 
modifications  of  neon  have  already  been  referred  to.  A  number 
of  experiments  to  this  end  have  already  been  carried  out  with 
other  elements,  and  doubtless  in  the  future  we  may  expect  much 
activity  in  the  same  direction.  It  also  appears  highly  desirable 
that  a  series  of  very  accurate  atomic  weight  determinations 
should  be  made  of  the  complex  elements  from  different  sources  to 


"  A  list  of  the  radioactive  isotopes  will  be  found  in  Appendix,  Table  B. 
"F.  W;  Aston,  Phil.  Mag.   (G)   40,  633  (1920). 


154  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

ascertain  if  the  isotopes  always  occur  mixed  in  the  same  pro- 
portion. 

No  attempt  to  separate  isotopes  has  as  yet  been  conclusively 
successful.  In  the  case  of  radioactive  and  ordinary  lead,  Rich- 
ards and  Hall  ^^  obtained  wholly  negative  results  by  the  use  of 
fractional  crystallization.  Harkins^^  and  his  co-workers  have 
been  engaged  in  the  attempt  to  separate  chlorine  by  diffusion 
and  have  obtained  encouraging  though  not  finally  positive  results. 
The  theoretical  aspects  of  the  separation  of  chlorine  by  various 
methods  have  been  the  subject  of  much  recent  discussion.^^ 

Bronsted  and  v.  Hevesy  ^®  report  the  separation  of  mercury 
into  two  fractions  by  distillation,  one  having  a  density  0.999980, 
the  other  of  1.000031,  compared  with  that  of  the  original  as 
unity. 

63.    General  Properties  of  Recoil  Atoms. 

The  treatment  of  the  chemical  action  produced  by  recoil 
atoms  does  not  fall  under  the  title  either  of  a  particles  or  elec- 
trons, but  since  the  emission  of  a  radiation  and,  to  a  much  smaller 
degree,  of  (3  radiation  is  always  accompanied  by  recoil,  and  since 
it  has  recently  been  shown  that  the  recoil  atoms  are  capable  of 
producing  chemical  action,  it  appears  appropriate  to  treat  the 
subject  briefly  in  the  present  monograph.  Before  proceeding  to 
the  chemical  effects  it  will  be  necessary  to  consider  the  more 
general  characteristics  of  recoil  atoms. 

When  a  radioactive  atom  emits  an  a  particle  in  a  given  direc- 
tion the  parent  atom,  or  atomic  residue,  receives  an  impulse  in 
the  opposite  direction,  which  has  very  aptly  been  termed  recoil. 
The  atom  receiving  the  recoil  is  termed  the  recoil  atom.  Recoil 
atoms  were  first  studied  by  Miss  Brooks,^^  by  Hahn,^^  and  by 
Russ  and  Makower  ^^  as  a  means  of  separating  the  recoiling 
radioactive  substance  in  a  pure  state. 

^T.  W.  Richards  and  N.  F.  Hall,  Joum.  Amer.  Chem.  Soc.  39,  531-41 
(1917). 

'«W.  D.  Harkins,  Science,  51,  289  (1920). 

"T.  R.  Merton  and  H.  Hartley,  Nature,  105,  104  (1920)  ;  W.  D.  Harkins, 
iiid.,  105,  230 ;  D.  L.  Chapman,  ihid.,  105,  487  ;  642  ;  F.  Soddy,  ibid.,  105,  516 ; 
A.  F.  Core,  ibid.,  105,  582. 

'■J.  N,  Bronsted  and  G.  v.  Hevesy,  Nature,  106,  144  (1920). 

"Miss  H.  T.  Brooks,  Nature,  July  21,  1904. 

"O.  Hahn,  Verh.  deut.  phys.  Qea.,  11,  55  (1009). 

"  S.  Russ  and  W.  Makower,  Proc.  Roy.  Soc.  82A,  205   (1909). 


I 


POSITIVE  RAYS  AND  RECOIL  ATOMS  155 

Rutherford  ^^  has  shown  that  when  a  particle  of  mass  m  is 
ejected  with  velocity  v  from  an  atom  of  mass  M,  the  residual 
atom  of  mass  M-m  recoils  with  a  velocity  V,  according  to  the 
relation  (M-m)  V  =  mv.  In  the  case  of  Ra  A  of  atomic  weight 
218  (Table  I)  the  expulsion  of  the  a  particle  of  mass  4  at  a 
velocity  of  1.82  x  10^  cms.  sec."^  results  in  a  recoil  atom  of  Ra  B 
with  a  velocity  of  3.4  x  10^  cms.  sec."^.  This  velocity  is  sufficient 
to  ionize  a  gas  in  which  the  recoil  radiation-  takes  place,  as 
has  been  shown  by  Wertenstein.^^  The  velocity  and  kinetic 
energy  of  the  recoil  atoms  may  be  calculated  to  be  about  1/50 
to  1/60  that  of  the  corresponding  a  particles.    The  fraction  in 

each  case  is  equal  to  ^hf -o^ 

^  M-m.  2* 

Wertenstein,^^  in  the  laboratory  of  Mme.  Curie,  has  made 
the  most  exhaustive  investigation  of  recoil  atoms  yet  under- 
taken. He  has  called  the  recoil  atoms  from  Ra  A  a  particles. 
They  have  a  range  in  air  at  atmospheric  pressure  of  0.14  mm., 
and  in  hydrogen  of  0.83  mm.  This  range  in  air  is  about  1/350 
that  of  the  a  particle ;  and  since  the  kinetic  energy  of  the  a  par- 
ticle is  1/50  that  of  the  a  particle,  it  is  evident  that  the  expendi- 
ture of  energy  by  the  a  particle  is  about  seven  times  as  great  per 
length  of  path  as  that  of  the  a  particle.  This  does  not  mean  that 
the  ionization  is  seven  times  as  great,  because  the  proportion  of 
energy  expended  in  producing  ionization  is  somewhat  smaller  in 
the  case  of  a  particles,  but  Wertenstein  found  that  the  ionization 
produced  by  a  particles  becomes  in  maxima  about  five  times  as 
great  as  that  of  a  particles  over  the  same  path. 

This  knowledge  of  recoil  atoms  will  suffice  at  least  for  a  pre- 
liminary survey  of  what  may  be  expected  if  they  produce  chem- 
ical action  in  anything  like  the  same  proportion  to  their  ionizing 
powers  that  a  particles  do.  The  two  most  prominent  properties 
to  be  kept  in  mind  are  their  very  limited  range  and  their  great 
intensity  of  action  within  that  range.  In  a  vessel  of  infinitely 
large  volume  in  which  the  a  particles  would  expend  all  their 
energy  in  the  gas  system  without  striking  the  wall,  the  compara- 
tive effect  of  the  recoil  atoms  would  be  less  than  2%,  or  very 

"E.  E.  Rutherford,  "Radioactive  Substances  and  Their  Radiations"  (19.13), 
p.  174. 

23  L.  Wertenstein,  Comp.  rend.  152,  1057   (1911). 

2*  Meyer  and  v.  Schweidler,  "Radioaktivitat"  (191G),  p.  139, 

?'  li.  Wertenstein,  Thcsw,  paris,  1913, 


156  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

small.  On  reducing  the  volume  or  pressure,  the  effect  of  the 
easily  absorbed  recoil  atoms  remains  constant,  while  the  a  par- 
ticles expend  part  of  their  energy  in  the  wall,  which  part  was 
shown  in  Chapter  VI  to  be  ineffective  in  producing  chemical 
action.  As  the  volume  is  further  diminished  the  a  particles 
have  still  shorter  paths  and  the  effect  of  the  recoil  atoms  becomes 
relatively  greater  and  greater.  In  very  small  volumes  and  at 
low  pressures  it  is  evident  that  the  ionizing  and  chemical  effects 
of  the  recoil  atoms  would  exceed  the  effect  of  a  particles  by  sev- 
eral fold.  That  this  is  exactly  the  case  found  experimentally  with 
respect  to  chemical  action  will  be  shown  in  the  following  section. 

64.    Chemical  Reaction  Produced  by  Recoil  Atoms. 

In  §  43  the  influence  of  the  size  of  the  reaction  vessel  on  the 
rate  and  extent  of  the  combination  of  hydrogen  and  oxygen  in 
equivalent  proportions  mixed  with  radium  emanation  was  dem- 
onstrated. The  general  law  found  experimentally  and  based  in 
principle  upon  the  average  path  of  a  particles  in  the  reaction 

vessel  is  for  spheres:  log  P/Po/Eofe-^'  —  1)  =  84.1/0^,  in  which 
Po  is  the  initial  pressure  of  electrolytic  gas  in  mm.  of  Hg,  P  the 
pressure  of  the  same  at  any  time  t,  Eo  is  the  initial  quantity  of 
radium  emanation  in  curies,  e"^^  expresses  the  rate  of  decay  of 
emanation,  and  D  is  the  diameter  of  the  spherical  reaction  vessel 
in  cms.  The  expression  was  shown  to  be  true  for  spheres  with 
diameters  up  to  about  10  cms.  containing  electrolytic  mixture 
not  exceeding  one  atmosphere  pressure.  On  attempting  to  apply 
the  kinetic  equation  represented  by  the  left  hand  side  of  the 
equation  just  given,  to  the  case  of  a  sphere  of  diameter  as  small 
as  1  cm.,  it  was  found  that  a  velocity  constant  could  not  be 
obtained  as  in  the  case  of  larger  spheres  (Table  XI).  The 
experimental  data  of  Lind  ^^  are  shown  in  Table  XIX  for  a 
sphere  of  about  1  cm.  diameter  which  should  have,  according  to 
the  general  relation  for  larger  spheres,  a  value  of  velocity  constant 
(k^i/X)  of  90.4,  but,  as  will  be  seen,  the  value  of  the  first  measure- 
ment was  104.6,  which  rose  as  the  reaction  progressed  to  a  value 
of  220.5.  If  the  velocity  constant  be  calculated  for  each  separate 
interval,  as  explained  in  §  45,  the  rise  of  the  (k^/X) '  becomes  still 
more  marked,  as  may  be  seen  in  the  table.    But  the  time  intervals 

JOS.  C.  Lind,  Journ.  Amcr.  Chem.  Soc.  41,  533  (li)ll)). 


POSITIVE  RAYS  AND  RECOIL  ATOMS 


157 


are  still  too  large.  To  avoid  this,  Curve  1  in  Fig.  7  was  plotted 
with  pressure  as  ordinates  and  time  as  abscissae.  The  interpo- 
lated values  of  P  in  Table  XIX  were  then  taken  from  the  curve 
from  which  the  values  of  (k^,/A)'  in  the  last  column  were  cal- 
culated. Curve  la  in  Fig.  7  shows  the  course  of  the  normal 
pressure  reduction  by  a  rays  alone  in  larger  vessels,  as  calculated 
from  the  general  equation. 


TABLE  XIX 

Effect  of  Recoil  Atoms  in  Producing  an  Abnormal  Rate  of  Com- 
bination of  Hydrogen  and  Oxygen  in  a  Small  Sphere 


Vol.  =  0.470  c.  c. 


Diam.  =  0.9647  cm.    Eo  —  0.04234  curie. 
Normal  k\i/l  =  90.4. 


Actual  Data 

Calculated  from 
Actual  Data 

Interpolated  Data 

Days 

Hrs. 

P.  in 
mm.  Hg 

k\i/k 

(k\i/ir 

Days 

Hrs. 
0.0 

P. 

(k\i/iy 

0 

0.0 

507.8 

0 

507.8 

0 

6.0 

425.0 

95.6 

0 

15.67 

310.3 

104.6 

104.6 

0 
0 

12.0 

18.0 

354.0 
290.0 

102.7 
117.1 

0 

19.90 

271.2 

105.9 

111.2 

1 
1 

0.0 
6.0 

233.0 
187.0 

134.4 
141.6 

0 

23.67 

235.1 

111.4 

142.9 

1 

1 

12.0 

18.0 

150.7 
123.0 

145.0 

148.8 

1 

15.33 

135.4 

121.4 

139.0 

2 
2 

0.0 
6.0 

96.0 
73.0 

182.4 
210.9 

1 

19.00 

119.0 

123.4 

148.7 

2 
2 

12.0 
18.0 

51.5 
33.0 

278.9 
377.6 

2 

5.00 

76.7 

134.8 

195.0 

3 
3 

0.0 
3.0 

19.5 
14.0 

461.7 
594.3 

3 

0.33 

18.8 

181.3 

349.6 

3 
3 

6.0 
9.0 

9.9 
7.5 

646.0 
528.5 

3 

15.42 

5.0 

220.5 

483.3 

3 
3 

12.0 
15.42 

5.7 
5.0 

535.1 
228.3 

To  ascertain  whether  the  abnormality  observed  for  the  1  cm. 
sphere  could  be  accounted  for  by  the  action  of  recoil  atoms  added 
to  that  of  a  particles,  the  following  analysis  of  the  results  was. 


158  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 


made.  If  90.4  is  the  normal  velocity  constant  for  a  particles, 
180.8  will  represent  a  velocity  where  the  action  of  recoil  atoms 
is  just  equal  to  that  of  a  particles  under  the  same  conditions. 
By  plotting  the  (k|x/X)'  values  from  the  last  column  of  Table 
XIX  as  Curve  2  of  Fig.  7,  it  was  found  that  (kjx/X)'  becomes 
equal  to  180.8  at  a  gas  pressure  of  118  mms.  At  any  other  pres- 
sure the  proportion  of  chemical  action  being  produced  by  each 
type  of  radiation  can  be  estimated  on  the  following  basis: 

1.  That  the  chemical  effect  of  the  recoil  atoms  remains  con- 
stant down  to  a  very  low  pressure  at  which  they  also  begin  to  reach 
the  wall  in  large  proportion  without  being  stopped  by  the  gas. 


/  2 

T/MS  IN  Days  for  all  Curves 
Fig.  7. 


2.  That  the  chemical  effect  of  the  a  particles  will  at  all  pres- 
sures be  proportional  to  the  pressure. 

For  example,  at  118  mms.  the  two  effects  are  equal  to  each 
other  and  one  can  arbitrarily  place  each  equal  to  118.  At  any 
other  pressure,  50  mms.  for  example,  the  recoil  atom  effect,  which 


I 


POSITIVE  RAYS  AND  RECOIL  ATOMS  169 

for  convenience  will  be  called  the  R  effect,  would  still  have  the 
value  118;  the  a  effect  now  will  have  the  value  50;  the  combined 
effect  is  168;  the  abnormality  factor,  or  the  ratio  of  the  observed 
abnormal  effect  to  the  normal  <x  effect,  will  be  (R  +  a)/a  = 
168/50  =  3.36.  Table  XX  shows  this  same  analysis  carried  to 
its  upper  and  lower  limits. 

Comparison  of  the  last  two  columns  of  Table  XX  shows  that 
the  general  trend  of  the  experimental  and  calculated  values  of 
the  velocity  constant  (kpi/^) '  is  the  same.  The  calculated  values 
will  be  found  plotted  in  Curve  2  of  Fig.  7  as  +,  the  interpolated 
values  taken  from  Table  XIX  as  O .  The  agreement  between 
theory  and  experiment  is  satisfactory.  The  maximum  value 
found,  632,  when  divided  by  the  normal  a  value  90.4,  shows  that 
the  maximum  ratio  (R  +  a) /a  is  6.99.  According  to  Wertenstein 
{loc.  cit.)  the  maximum  ionization  due  to  recoil  atoms  from 
Ra  A  is  five  times  that  of  the  a  particles  over  the  same  path, 
which  would  be  a  combined  ionization  six  times  that  of  the  a 
particles  alone.  Remembering  that  Wertenstein's  statement 
refers  to  recoil  atoms  from  Ra  A  alone,  while  with  emanation 
we  are  dealing  with  three  different  sets  of  a  particles,  the  agree- 
ment is  perhaps  as  good  as  could  be  expected.  At  least  one  must 
be  convinced  that  recoil  atoms  cause  the  combination  of  hydro- 
gen and  oxygen  at  ordinary  temperature,  and  approximately  in 
the  same  proportion  to  their  ionizing  powers  as  in  the  case  of  a 
particles. 

At  first  thought  it  must  appear  surprising  that  the  chemical 
effect  of  recoil  atoms  can  be  observed  at  fairly  large  pressures. 
One  must  consider,  however,  that  the  radius  of  the  reaction  bulb 
is  only  4.8  mms.,  and  that  the  average  path  within  the  spherical 
bulb  is  only  about  6/10  of  this,  or  about  2.9  mms.;  moreover,  the 
range  of  the  a  particle  in  the  electrolytic  mixture  will  be  about 
0.3  nam.  at  standard  pressure  (calculated  from  Wertenstein's 
measurements  for  air  and  for  hydrogen),  and  would  be  still 
greater  for  recoil  atoms  of  Ra  C.  These  facts,  considered  together 
with  the  intensity  of  the  energy  expense  by  recoil  atoms,  make  it 
evident  that  the  pressure  and  bulb  dimensions  at  which  the 
chemical  effect  of  recoil  atoms  manifests  itself  are  quite  con- 
cordant with  Wertenstein's  ionization  data. 

Finally  it  should  be  inquired  whether  the  chemical  effect  of 
recoil  atoms  will  not  also  be  observed  in  larger  spheres  at  low 


160  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

pressure.  The  answer  must  be  affirmative,  with  certain  reserva- 
tions. By  referring  to  Table  XI  it  will  be  seen  that  for  the  2- 
centimeter  sphere  there  is  an  unmistakable  tendency  for  k|x/X 
to  increase  slightly  toward  the  end  of  the  reaction,  which  tend- 
ency would  be  brought  out  much  more  distinctly  by  calculating 
for  (kjx/X)'.  However,  the  quantity  of  gas  to  be  acted  on  in 
larger  spheres,  beginning  with  normal  pressure,  is  so  much  greater 
than  in  a  1-cm.  one,  that  before  low  pressures  are  attained,  the 
emanation  is  nearly  exhausted  and  the  effect  on  the  k\i/k  value 
is  largely  masked. 

TABLE  XX 

Analysis  of  the  Recoil  Atom  Effect  (R)  and  the  a  Ray  Effect  (a) 
in  Causing  Electrolytic  Hydrogen  and  Oxygen  to  Combine 
in  a  1  cm.  Sphere 

R  effect  =  constant  =118.  a  effect  proportional  to  pressure  =  P. 


a  =  P  (mm.  Hg) 

R  +  o. 

(R  + «;/« 

(k\i/iy 

Calcd. 

(h\i/iy 
Found 

(Curve  2) 

10 

128 

(12.80) 

... 

20 

138 

6.90 

622 

632 

30 

148 

4.93 

444 

446 

40 

158 

3.95 

356 

376 

50 

168 

3.36 

303 

350 

60 

178 

2.97 

268 

292 

70 

188 

2.69 

242 

267 

80 

198 

2.48 

223 

240 

90 

208 

2.31 

208 

223 

100 

218 

2.18 

195 

204 

110 

228 

2.07 

186 

192 

120 

238 

1.98 

177 

182 

130 

248 

1.91 

172 

166 

140 

258 

1.84 

166 

162 

160 

268 

1.79 

161 

153 

200 

318 

1.59 

143 

133 

250 

368 

1.47 

132 

118 

300 

418 

1.39 

125 

112 

400 

518 

1.29 

116 

100 

500 

618 

1.24 

113 

95 

600 

718 

1.19 

107 

... 

POSITIVE  RAYS  AND  RECOIL  ATOMS  161 

The  almost  vertical  drop  in  Curve  2,  Fig.  7,  after  passing  the 
maximum  is  due  to  practical  exhaustion  of  the  electrolytic  gas 
mixture.  The  experimental  method  employed  was  the  same  as 
that  described  in  §  42,  and  is  not  applicable  to  extremely  low 
pressures  with  accuracy.  It  would  be  very  interesting  to  exam- 
ine this  reaction,  using  a  refined  pressure  method  in  order  to 
investigate  more  precisely  the  course  of  the  reaction  near  its 
end.  Theoretically  the  abnormality  factor  should  continue  to 
rise  until  the  gas  is  completely  exhausted. 


Chapter  12. 
Atomic  Disintegration  by  a  Particles. 

65.    Scattering  and  Impacts  of  a  Particles. 

The  great  potency  of  the  a  particle  as  an  agent  in  the  produc- 
tion of  chemical  action  has  been  frequently  emphasized  in  pre- 
ceding chapters.  The  reactions  treated  up  to  the  present  have 
been  of  ordinary  molecular  character.  Very  recently  Rutherford 
has  demonstrated  conclusively  for  the  first  time  that  under  cer- 
tain conditions  the  a  particle  is  capable  of  producing  a  much  more 
fundamental  chemical  change,  namely,  the  disintegration  of  the 
atom  into  new  kinds  of  atoms.  Although  such  changes  are  spon- 
taneously taking  place  among  the  radioactive  elements,  Ruther- 
ford has  presented  the  first  evidence  that  can  be  accepted  with- 
out doubt,  of  the  artificial  disintegration  of  the  atom.  These 
intra-atomic  reactions  fall  very  properly  within  the  confines  of 
radiochemistry.  It  will  therefore  be  attempted  to  give  a  brief 
non-mathematical  description  of  Rutherford's  work  which  led 
up  to  and  proved  absolutely  this  discovery  of  preeminent 
importance. 

The  investigations  of  Rutherford  and  his  co-workers  in  Man- 
chester and  more  recently  in  Cambridge  of  the  phenomena 
accompanying  the  passage  of  a  particles  through  matter  have 
been  remarkably  successful  in  furnishing  insight  into  the  question 
of  atomic  structure.  As  has  been  pointed  out,  the  flight  of  the 
a  particle  of  high  velocity  carries  it  in  a  straight  line  through 
a  large  number  of  molecules  or  atoms,  which  are  ionized  by  the 
removal  of  a  single  electron  from  each  molecule  encountered. 
The  a  particle  suffers  no  deflection  in  the  ordinary  encounter, 
but  has  its  velocity  gradually  diminished  until  it  is  no  longer 
able  to  produce  ionization.  Toward  the  end  of  its  path,  when 
its  velocity  is  much  reduced,  the  a  particle  is  more  subject  to 
deflection  or  scattering,  and  occasionally  it  experiences  a  very 
large  deflection  or  is  actually  turned  backward  in  its  path.    The 

162 


ATOMIC  DISINTEGRATION  BY  a    PARTICLES  163 

great  rarity  of  the  occurrence  of  the  large  deflections  led,  as  has 
already  been  pointed  out,  to  the  Rutherford-Bohr  atomic  model 
according  to  which  most  of  the  atomic  mass  is  centered  in  an 
extremely  minute  nucleus  with  a  positive  charge  equal  to  the 
atomic  number  of  the  atom,  which  for  the  heavier  elements  is 
somewhat  less  than  half  the  atomic  weight. 

The  large  deflections  or  reversals  of  the  a  particle  are  then 
attributed  to  a  close  impact  of  the  particle  with  the  nucleus  of 
the  atom  encountered.  These  impacts  were  first  investigated 
using  thin  sheets  of  the  heavier  metals.  The  law  governing  the 
deflection  or  scattering  was  worked  out  by  Geiger  and  Marsden,^ 
on  the  basis  of  repulsion  inversely  with  the  square  of  the  distance 
from  point  charges.  The  experimental  scattering  was  in  good 
agreement  with  this  theory  and  it  was  calculated  that  the  direct 
impact  represents  an  approach  of  the  a  particle  to  the  nucleus 
within  about  3  x  10"^^  cm.  in  the  case  of  heavy  atoms. 

The  case  for  light  atoms  is  different  in  two  important  respects. 
First,  on  account  of  the  smaller  nuclear  charge  the  repulsion  of 
the  positively  charged  a  particle  is  much  less  than  in  the  case 
of  heavy  atoms,  and  the  a  particle  is  therefore  able  to  approach 
much  closer  to  the  nucleus,  approximately  ten  times  as  close. 
This  close  approach  on  impact  produces  radical  differences  in 
the  result  of  the  repulsion  which  will  be  described  later.  Second, 
on  account  of  the  smaller  mass  of  the  nucleus  of  light  atoms 
they  are  repelled  to  greater  distances  than  the  heavy  ones. 
Under  favorable  circumstances  the  light  atoms  are  projected 
forward  at  a  velocity  which  carries  them  beyond  the  range  of  the 
impelling  a  particle  and  can  be  detected  and  counted  by  the 
scintillation  method.  This  opens  new  possibilities  for  their  inves- 
tigation, which  have  been  utilized  by  Rutherford  as  will  be 
recounted  in  the  following  paragraphs. 

Darwin  ^  has  shown  that  the  law  of  scattering  and  repulsion 
predicts  that  all  the  light  atoms  up  to  and  including  oxygen 
should  be  capable  of  being  repelled  by  a  doubly  charged  a  par- 
ticle to  a  distance  exceeding  the  range  of  the  a  particle  in  the 
same  medium,  provided  that  the  atom  repelled  has  a  single 
positive  charge.  Evidently,  if  the  repelled  atom  has  a  double 
charge,  no  atom  heavier  than  helium  could  be  repelled  beyond 

iH.   Geiger   and   E.   Marsden,  Phil.  Mag.    (6)    25,   604    (1913). 
*C.  G.  Darwin,  PJiil.  Mag.   (6)   27,  499   (1914). 


164  THE  CHEMICAL  EFFECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

the  range  of  the  a  particle,  without  borrowing  energy  from  some 
other  source.  It  was  to  test  this  prediction  that  Rutherford 
undertook  the  experiments  which  have  led  to  other  highly  sig- 
nificant conclusions. 

66.     Swift  Hydrogen  Atoms. 

In  the  case  of  the  repulsion  of  a  hydrogen  atom  as  the  result 
of  an  intimate  impact  with  an  a  particle,  we  have  a  case  of  great 
simplicity  in  some  respects.  On  account  of  its  having  but  a 
single  electron  it  is  impossible  for  the  nucleus  of  the  hydrogen 
atom  to  carry  more  than  a  single  positive  charge.  On  account 
of  its  elemental  nature  there  is  little  probability  of  the  hydrogen 
atom  being  changed  or  disrupted  by  impact  with  an  a  particle. 
On  the  theory  of  impact  one  should  expect  a  hydrogen  atom  to 
be  set  into  swift  motion  as  the  result  of  a  direct  nuclear  encoun- 
ter with  an  a  particle,  with  a  velocity  1.6  times  that  of  the  a 
particle.  The  range  to  be  expected  for  the  swift  hydrogen  atom 
would  be  about  four  times  that  of  the  a  particle,  and  its  kinetic 
energy  0.64  of  the  energy  of  the  a  particle.  Marsden  ^  found  that 
the  passage  of  a  particles  through  hydrogen  did  produce  a  large 
number  of  faint  scintillations  on  a  zinc  sulfide  screen  which 
could  be  detected  far  beyond  the  range  of  the  a  particle.  Ruther- 
ford* has  made  a  very  detailed  study  of  the  subject  which  con- 
firmed the  theoretical  predictions.  The  swift  H  atoms  have  a 
range  in  hydrogen  of  100  cms.,  about  four  times  that  of  the  a 
particle  in  the  same  gas.  The  nimiber  projected  straight  forward 
by  an  <x  particle  of  range  7  cms.  is  30  times  greater  than  required 
by  the  simple  theory  of  scattering.  The  probable  explanation  is 
the  distortion  of  the  nucleus  by  such  close  approach,  which  was 
about  3  x  10"^^  cm.,  or  approximately  the  same  as  the  diameter  of 
an  electron.  The  direction  of  the  swift  H  atoms  is  mainly  the 
same  as  that  of  the  a  particle,  and  the  velocity  of  different  par- 
ticles is  uniform.  On  reducing  the  velocity  of  the  a  particle  the 
direction  of  the  H  atoms  becomes  more  varied,  approaching  the 
requirements  of  the  law  of  scattering  as  to  distribution,  but  still 
exceeding  theory  in  number.  In  traversing  one  cm.  of  hydrogen 
about  lO'*  a  particles  produce  one  swift  H  atom,  which  means 

»E.    Marsden,    Phil.   Mag.    (G)    27,    824    (1914).      E.    Marsden    and    W.    C. 
Lantsberry,  ibid.,  30,  240   (1915). 

*E.  E.  Rutherford,  Phil.  Mag.   (C)   37,  537-61;  5G2-71    (1919). 


ATOMIC  DISINTEGRATION  BY  a    PARTICLES  165 

that  out  of  10^  hydrogen  atoms  ionized,  only  1  is  set  into  swift 
motion  as  the  result  of  a  direct  nuclear  impact. 

Since  the  nuclear  impact  is  an  atomic  phenomenon,  the  long 
range  swift  atoms  can  be  produced  by  radiating  either  the  ele- 
ment or  any  compound  of  it.  This  fact  has  proved  a  source  of 
some  embarrassment  in  the  case  of  hydrogen,  since  it  is  very 
difficult  to  remove  water  vapor  and  possibly  other  compounds 
containing  hydrogen  from  the  field  of  action.  As  a  consequence 
every  source  of  a  radiation  has  been  found  to  give  some  swift  H 
atoms  continuously.  So  persistent  is  this  phenomenon  that  it 
has  suggested  the  possibility  of  the  emission  of  H  particles  from 
the  nucleus  of  the  radioactive  element  itself  in  the  same  way  that 
a  particles  are  emitted.  Later  evidence  obtained  by  Rutherford 
{loc.  cit.)  does  not  appear  to  support  such  an  hypothesis  strongly, 
but  the  question  is  still  regarded  by  Rutherford  as  a  subject 
requiring  further  investigation. 

Both  magnetic  and  electrostatic  methods  of  deflection  have 
been  used  by  Rutherford  in  examining  the  charge  and  velocity 
of  the  swift  H  atoms.  The  charge  was  shown  to  be  unipolar 
positive,  and  the  maximum  velocity  is  1.6  times  that  of  the  a 
particle,  as  required  by  theory. 

67.     Experiments  of  Rutherford  with  Other  Light  Atoms. 

After  obtaining  such  important  results  with  hydrogen  Ruther- 
ford ^  proceeded  to  investigate  the  propulsion  of  some  of  the 
other  light  atoms  to  distances  beyond  the  range  of  the  a  parti- 
cle. Assuming  singly  charged  particles  as  the  result  of  impact, 
it  was  predicted  from  Darwin's  formulation  that  the  swift  nitro- 
gen atom  ought  to  have  a  range  1.33  times  that  of  the  a  particle 
producing  it,  and  that  oxygen  should  similarly  have  the  value 
1.12.  Both  of  these  gases  were  examined  by  Rutherford,  who 
found  numerous  scintillations  beyond  the  a  range  in  the  region 
7-9  cms.  from  the  source,  which  in  number  corresponded  closely 
to  that  found  in  the  hydrogen  experiments,  indicating  that  the 
nature  of  the  impact  was  similar.  The  range  found  for  nitrogen 
was  approximately  that  predicted  by  theory.  In  the  case  of 
oxygen  the  range  was  not  very  different  from  that  found  for 
nitrogen.     This  value  greater  than  theory  was  rather  puzzling, 

•E.   E.   Rutherford,  Phil.  Mag.   (6)    37,  571-87   (1919). 


166  THE  CHEMICAL  EFFECTS  OF  AlPHA  PARTICLES  A^D  ELECTRO^ 

but  Rutherford  was  inclined  to  believe  that  the  swift  particles 
were  in  both  cases  the  singly  charged  oxygen  or  nitrogen  atoms. 
The  improbability  of  this  assumption  was  pointed  out  by 
Fulcher,®  who  showed  that  the  propulsion  of  a  singly  positively 
charged  atom  of  nitrogen  (or  oxygen)  involves  the  assumption 
that  the  other  orbital  electrons  are  carried  with  the  swift  atom. 
According  to  Fulcher's  contention  the  forces  binding  these  remote 
electrons  to  the  nucleus  are  not  sufficient  to  overcome  their  initial 
inertia  at  the  moment  of  impact,  when  they  would  have  to  take 
on  a  speed  of  10^  cm.  sec.-^  in  less  than  10~^^  sec.  According  to 
Fulcher  the  remaining  electrons  would  either  be  left  behind  ini- 
tially or  soon  be  brushed  off  by  contact  with  other  molecules  of 
the  gas  traversed.  The  swift  particles  could  not  be  nitrogen  or 
oxygen  atoms  without  electrons,  for  such  multiply  charged  atoms 
would  have  shorter  ranges  than  were  observed.  Fulcher  suggests 
that  the  swift  particles  are  a  rays  produced  by  the  disruption  of 
nitrogen  by  the  impact.  Of  course  doubly  charged  helium  atoms 
could  not  be  projected  beyond  the  range  of  the  bombarding  a 
particle  unless  they  got  additional  energy  from  some  other  source. 
Fulcher  suggested  that  the  impact  results  in  the  explosion  of  the 
nitrogen  atom  so  that  the  internal  atomic  energy  becomes  avail- 
able, just  as  in  the  case  of  the  radioactive  changes.  This  would 
represent  a  type  of  "artificial  radioactivity"  which  will  be  dis- 
cussed in  §  69.  The  only  difficulty  of  Fulcher's  assumption  lay 
in  its  failing  to  explain  the  uniform  direction  of  the  swift  parti- 
cles in  the  direction  of  the  a  particle.  The  result  of  an  atomic 
explosion  would  be  expected  to  cause  the  ejection  of  a  particles 
in  any  direction  according  to  the  law  of  chance.  The  probability 
of  atomic  disruption  by  a  particles  had  already  been  established 
for  nitrogen  in  another  way  by  Rutherford,  which  will  be  con- 
sidered in  the  following  section. 


68.    Decomposition  of  Nitrogen  and  Oxygen. 

In  June  1919  Rutherford  ^  reported  the  observation  of  an 
anomalous  effect  in  nitrogen  bombarded  by  a  rays.  A  closed 
metal  box  containing  an  intense  source  of  Ra  C  at  3  cms.  from 
the  end  was  provided  with  an  opening  in  the  end  covered  with  a 
silver  plate  of  stopping  power  equivalent  to  6  cms.  of  air.    The 

•G.  S.   Fulcher,  Science  r»0,  582-4    (1919). 
»E.  E.   Rutherford,  Phil.  Mag.   (6)    37,  581-7. 


ATOMIC  DlSlKTEaRATlON  BY  a    PARTICLES  167 

ZnS  screen  was  placed  just  outside  the  opening  at  1  mm.  dis- 
tance. The  number  of  "natural"  scintillations  on  this  screen, 
owing  to  some  unavoidable  source  of  swift  H  atoms,  is  increased 
by  exhausting  the  box.  On  admitting  dry  air  or  CO2,  the  num- 
ber of  scintillations  is  diminished  in  the  ratio  to  be  expected  from 
the  increase  of  stopping  power  of  the  gas  column.  But  if  nitrogen 
is  admitted  the  number  of  scintillations  increases.  Nitrogen  from 
different  sources  was  tried  and  various  attempts  were  unsuccess- 
ful in  explaining  the  phenomenon  without  assuming  that  H  atoms 
were  being  bombarded  from  nitrogen  atoms  by  a  rays.  The 
observed  range  of  the  swift  particles  was  too  great  for  them  to 
have  a  mass  greater  than  that  of  the  H  atom ;  the  effect  seemed  to 
depend  on  the  presence  of  nitrogen  and  to  be  proportional  to  its 
concentration,  so  that  no  other  conclusion  was  left  open  except 
that  nitrogen  is  disrupted  by  a  ray  bombardment  and  that  one 
of  the  products  of  the  disruption  is  the  swift  H  atom. 

Upon  going  to  Cambridge,  Rutherford^  continued  his  work 
on  the  nuclear  constitution  of  atoms,  and  devised  a  comparison 
method  of  examining  the  magnetic  deflection  of  the  swift  parti- 
cles in  order  to  estimate  the  mass.  The  results  of  the  experiments 
confirm  that  the  long  range  particles  from  nitrogen  are  particles 
with  the  same  mass  as  the  H  atom,  as  Rutherford  had  previously 
supposed.  The  investigation  of  the  shorter  range  particles  from 
oxygen  and  nitrogen  has  in  part  confirmed  the  predictions  of 
Fulcher.  In  both  cases  they  appear  to  be  doubly  charged  helium 
atoms  and  not  the  singly  charged  atom  of  nitrogen  or  oxygen; 
but  instead  of  having  the  usual  mass  4  of  the  He  atom,  a  mass  of 
3  was  found  which  according  to  Rutherford  represents  an  isotope 
of  helium.  In  the  case  of  oxygen  no  very  long  range  particles 
corresponding  to  those  of  hydrogen  and  nitrogen  are  found,  and 
Rutherford  suggests  that  the  oxygen  nucleus  is  composed  of  four 
helium  atoms  of  mass  3  and  one  of  mass  4  and  two  nuclear  or 
binding  electrons  giving  a  net  positive  charge  of  8.  In  the  case  of 
nitrogen  we  have  two  different  modes  of  disruption,  one  giving 
swift  doubly  charged  atoms  of  helium  of  mass  3,  the  other  giv- 
ing swift  H  atoms  of  mass  1.  Since  the  number  of  the  former 
exceeds  the  latter  by  five  to  ten  fold,  Rutherford  assumes  that 
the  two  modes  of  disruption  are  independent  of  each  other  and 
do  not  occur  simultaneously  from  the  same  atom.    The  nuclear 

"E.  E.  Rutherford,  Bakerian  Lecture,  Proc.  Roy.  Soc.  97A,  374-400   (1920). 


16S  THE  CHEMICAL  EPEECTS  OF  ALPHA  PARTICLES  AND  ELECTRONS 

structure  of  nitrogen  proposed  by  Rutherford  is  four  doubly 
charged,  helium  atoms  of  mass  3  and  two  singly  charged  H  atoms 
of  mass  1  and  three  binding  electrons  giving  a  net  positive  charge 
of  7.  If  the  H  atoms  have  an  interior  position  in  the  nucleus 
with  reference  to  the  He  atoms,  as  Rutherford  suggests,  this 
might  account  for  the  greater  frequency  of  the  disruption  accom- 
panied by  expulsion  of  a  swift  He  atom. 

69.    Artificial  Radioactivity. 

The  experimental  results  of  Rutherford  just  discussed  in  §  68 
appear  to  confirm  Fulcher's  prediction  (§  67)  that  the  shorter 
range  swift  particles  from  nitrogen  (and  also  those  from  oxygen) 
are  not  the  singly  charged  N  and  0  atoms,  but  are  doubly  charged 
He  atoms  (of  mass  3).  Rutherford  estimates  that  the  gain  in 
energy  of  motion  resulting  from  the  impact  must  be  at  least  8%, 
even  though  the  subsequent  motion  of  the  disintegrated  nucleus 
and  of  the  bombarding  a  particle  be  neglected.  Evidently  this 
additional  energy  is  derived  from  the  internal  atomic  energy 
of  the  disrupted  atom,  and  we  have  direct  proof  of  Fulcher's 
"artificial  radioactivity."  If  the  excess  energy  utilized  by  the 
swift  particle  is  in  reality  not  more  th|in  8%  of  the  energy  of 
the  bombarding  a  particle,  Fulcher's  difficulty  of  explaining  the 
uniform  direction  of  the  swift  particles  can  perhaps  be  dismissed. 
There  is  no  evidence  that  the  atomic  nucleus  is  entirely  disrupted, 
and  Rutherford  inclines  to  the  view  that  only  a  single  particle 
is  ejected  from  each  atom  and  discusses  the  possible  isotopic 
modifications  of  atoms  of  lower  atomic  weight  which  remain  as 
the  result  of  the  loss  of  a  single  atom  in  the  two  types  of  disrup- 
tion. As  yet  there  is  experimental  evidence  only  of  the  swift 
particles  of  range  longer  than  the  a  particle  and  we  have  no 
direct  evidence  as  to  the  nature  of  the  residue. 

Rutherford  points  out  that  the  amount  of  disintegration  is 
exceedingly  small.  If  in  the  case  of  nitrogen  only  one  a  particle 
in  300,000  succeeds  in  getting  near  enough  to  the  nucleus  to 
liberate  a  swift  H  atom  with  sufficient  velocity  for  it  to  be 
detected,  the  entire  a  radiation  from  a  gram  of  radium,  if  wholly 
absorbed  in  nitrogen,  would  generate  only  about  5  x  10"*  mm.*  of 
hydrogen  per  year.  It  is  quite  possible  however  that  much  dis- 
integration takes  place  through  the  liberation  of  particles  of 


ATOMIC  DISINTEGRATION  BY  a    PARTICLES  169 

slower  velocity  which  can  not  be  detected.  It  is  also  possible 
that  high  velocity  electrons  possess  sufficient  energy  to  bring 
about  such  a  disintegration,  because  their  close  approach  to, the 
nucleus  would  be  accompanied  by  an  attraction  instead  of  a 
repulsion.  In  this  case  we  should  expect  to  find  the  effect  pos- 
sibly more  pronounced  in  the  case  of  the  atoms  of  high  atomic 
number  than  of  lower.  It  is  possible  that  some  of  the  inert  gases 
found  by  various  authorities  by  spectral  methods  may  have 
resulted  from  intense  electronic  bombardment  of  the  electrodes. 
The  results  of  further  experiments  in  this  direction  may  be 
awaited  with  a  great  deal  of  interest.  Rutherford  does  not  con- 
sider it  impossible  that  penetrating  X  rays  may  have  sufficient 
energy  to  cause  atomic  disintegration. 

It  may  not  be  without  interest  to  observe  that  the  discovery 
of  radioactivity  came  about  as  the  result  of  the  search  for  the 
spontaneous  emission  of  X  rays.  We  now  have  the  situation 
reversed;  having  discovered  radioactivity  and  the  spontaneous 
disintegration  of  the  atom,  we  turn  back  to  its  artificial  dis- 
ruption, and  enter  upon  an  era  of  renewed  activity  in  the  quest 
of  "transmutation." 


170 


APPENDIX 


APPENDIX 
Table  A.     Decay  of  Radium  Examination  According  to  L.  Kolowrat 


Time 

Quantity 

Time 

Quantity 

A 

Time       1 

Quantity 

Remaining 

A 

Remaining 

Remaining 

A 

Days 

Bra. 

0.00 

Days 

Hrs. 

0.00 

Days 

Hrs. 

0.00 

0 

1.00000 

375 

11 

0.76913 

575 

8 

0.47592 

353 

0.5 

0.99625 

372 

12 

0.76338 

570 

6 

0.46533 

345 

1 

0.99253 

742 

13 

0.75768 

567 

9 

0.45498 

337 

2 

0.98511 

736 

14 

0.75201 

562 

12 

0.44486 

330 

3 

0.97775 

730 

15 

0.74639 

557 

15 

0.43496 

323 

4 

0.97045 

726 

16 

0.74082 

554 

18 

0.42528 

315 

6 

0.96319 

719 

17 

0.73528 

549 

21 

0.41582 

308 

6 

0.95600 

715 

18 

0.72979 

545 

0 

0.40657 

3004 

7 

0.94885 

709 

19 

0.72434 

542 

5 

4 

0.39455 

2915 

8 

0.94176 

703 

20 

0.71892 

537 

5 

8 

0.38289 

2829 

9 

0.93473 

699 

21 

0.71355 

533 

5 

12 

0.37158 

2745 

10 

0.92774 

693 

22 

0.70822 

529 

5 

16 

0.36059 

2664 

11 

0.92081 

688 

23 

0.70293 

525 

5 

20 

0.34994 

2585 

12 

0.91393 

683 

2 

0 

0.69768 

522 

6 

0 

0.33960 

2509 

13 

0.90710 

678 

2 

1 

0.69246 

517 

6 

4 

0.32956 

2435 

14 

0.90032 

672 

2 

2 

0.68729 

514 

6 

8 

0.31982 

2363 

15 

0.89360 

668 

2 

3 

0.68215 

509 

6 

12 

0.31037 

2293 

16 

0.88692 

663 

2 

4 

0.67706 

504 

6 

16 

0.30019 

2225 

17 

0.88029 

657 

2 

6 

0.66698 

490 

6 

20 

0.29229 

2160 

18 

0.87372 

653 

2 

8 

0.65705 

489 

0 

0.28365 

2096 

19 

0.80719 

648 

2 

10 

0.64726 

482 

4 

0.27527 

2034 

20 

0.86071 

643 

2 

12 

0.63763 

475 

8 

0.26714 

1974 

21 

0.85428 

639 

2 

14 

0.62813 

468 

12 

0.25924 

1915 

22 

0.84789 

633 

2 

16 

0.61878 

461 

16 

0.25158 

1859 

23 

0.84156 

629 

2 

18 

0.60957 

454 

20 

0.24414 

1804 

0 

0.83527 

624 

2 

20 

0.60050 

447 

8 

0 

0.23693 

1751 

1 

0.82903 

620 

2 

22 

0.59156 

440 

8 

4 

0.22993 

1699 

2 

0.82283 

614 

3 

0 

0.68275 

432 

8 

8 

0.22313 

1649 

3 

0.81669 

611 

3 

8 

0.56978 

422 

8 

12 

0.21654 

1600 

4 

0.81058 

605 

3 

6 

0.55711 

413 

8 

16 

0.21014 

1553 

5 

0.80453 

601 

3 

9 

0.54471 

404 

8 

20 

0.20393 

1507 

6 

0.79852 

597 

3 

12 

0.53259 

395 

9 

0 

0.19790 

1462 

1 

0.79255 

592 

3 

15 

0.52074 

386 

9 

4 

0.19205 

1419 

8 

0.78663 

588 

3 

18 

0.50916 

378 

9 

8 

0.18637 

1377 

9 

0.78075 

583 

3 

21 

0.49783 

369 

9 

12 

0.18087 

1326 

10 

0.77492 

579 

4 

0 

0.48676 

361 

9 

18 

0.17291 

1268 

I 


APPENDIX 


171 


Table  A. 


APPENDIX— (Con  fiTiwed) 
Decay  of  Radium  Examination  According  to  L.  Kolowrat 


Time 

Quantity 

Time 

Quantity 

Time 

Quantity 

Remaining 

A 

Remaining 

A 

Remaining 

A 

Days 

Hrs. 

e-^' 

0.00 

Days 

Hrs. 

0.00 

Days 

Hrs. 

0.00 

10 

0 

0.16530 

1212 

14 

16 

0.07136 

0519 

21 

12 

0.02086 

01496 

10 

6 

0.15803 

1159 

15 

0 

0.06721 

0489 

22 

0 

0.01906 

01367 

10 

12 

0.15107 

1108 

15 

8 

0.06329 

0461 

22 

12 

0.01742 

01250 

10 

18 

0.14442 

1059 

15 

16 

0.05961 

0434 

23 

0 

0.01592 

01142 

11 

0 

0.13807 

1013 

16 

0 

0.05613 

0409 

23 

12 

0.01455 

01044 

11 

6 

0.13199 

0968 

16 

8 

0.05287 

0385 

24 

0 

0.01330 

00954 

11 

12 

0.12619 

0925 

16 

16 

0.04979 

0362 

24 

12 

0.01216 

00872 

tl 

18 

0.12063 

0885 

17 

0 

0.04689 

0341 

25 

0 

0.01111 

00797 

12 

0 

0.11533 

0846 

17 

8 

0.04416 

0321 

25 

12 

0.01015 

00728 

12 

6 

0.11025 

0809 

17 

16 

0.04159 

0303 

26 

6 

0.00928 

00637 

12 

12 

0.10540 

0773 

18 

0 

0.03916 

02809 

27 

0 

0.00775 

00532 

12 

18 

0.10076 

0739 

18 

12 

0.03579 

02567 

28 

0 

0.00647 

00444 

13 

0 

0.09633 

0701 

19 

0 

0.03271 

02346 

29 

0 

0.00541 

00371 

13 

8 

0.09072 

0660 

19 

12 

0.02990 

02144 

30 

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0.00452 

13 

16 

0.08543 

0622 

20 

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0.02732 

01960 

40 

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0586 

20 

12 

0.02497 

01791 

50 

0 

0.000123 

14 

8 

.  0.07577 

0552 

21 

0 

0.02282 

01637 

0 

o 

0.00000 

172 


APPENDIX 


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INDEX  OF  SUBJECTS 


Absorption,  of  a  rays,  32,  33 ;  of  j8 
rays,  41  ;  of  7  rays,  45  ;  of  hydrogen 
in  glass  under  a  radiation,  112  ;  of 
xenon  (chemical?),  127;  infra-red  of 
methyl  acetate.  144. 

Acceptor,  photochemical,  133. 

Acetone,  photo-hydrolysis  of,  136,  145. 

Actinium  series,  23. 

Active,  deposit,  —  equilibrium  with 
emanation,    25  ;    —    properties,    35 ; 

—  heat  evolution,  65  ;  centers  of 
luminescence,  54  ;  —  recovery  theory 
of,  54 ;  deposit,  diffusion  and  loca- 
tion    of,    105 ;    —    hydrogen,    112 ; 

—  molecules,  143  ;  —  non-existence 
of,  143. 

Alkaline  halides,  decomposition  of  by 
penetrating  rays,  62 ;  —  sulfides, 
phosphorescence  of,  57. 

Alpha  Particle,  positive  charge,  22 ; 
corpuscular  nature.  22  ;  as  chemical 
agent.  22,  73,  92,  97  ;  kinetic  energy, 
26  ;  identity  of  from  various  sources, 
26  ;  range,  end  of,  27  ;  in  minerals, 
51  ;  radiometric  determination  of 
range,  77  :  velocity,  28  ;  equation  of, 
31  ;  unit  ionization  by,  29,  81,  116  ; 
enumeration  of,  31,  79  :  distribution 
in  time  and  space,  36 ;  ionization 
curve  of.  30.  79 ;  stopping  power 
toward,  32,  33 ;  change  of  valence 
by  emission  of,  42  ;  heat  of  absorp- 
tion, 65  ;  decomposition  of  ammonia 
by,  73,  85,  93,  97 ;  of  other  gases, 
85,  92,  93,  97 ;  ozonization  by,  75, 
85,  113  ;  thin  bulbs,  penetrable  by, 
76,  80 ;  number  from  radium,  79 ; 
average  path  of  in  spheres,  82  ;  syn- 
thesis of  hydrogen  chloride  by,  85  ; 
equilibrium  of  water  when  radiated 
by,  91,  104 ;  specific  ionization  of 
gases  by,  92 ;  comparison  of  chem- 
ical effect  of  penetrating  rays  with 
that  of.  112:  thermal  theory  of 
chemical  effect,  116 ;  recoil  atoms 
from,  154 ;  atomic  disruption  by, 
162;  scattering  by,  163. 

Ammonia,  decomposition  by  a  particles, 
72.  85,  93,  98 ;  by  electrical  dis- 
charge,  126  ;   equilibrium  of,   72.  73. 

Analysis,  positive  ray  method,  149  ;  of 
chemical  effect  of  recoil  atoms,  157. 

Anthracene,  photochemical  polymeriza- 
tion of,  134. 

Argon,  two  isotopes  of,  153. 

Arsenic,  simple  element,  153. 

Atom,  radioactive  disintegration,  21, 
24 ;  -ic  weight  change  by  emission 
of  an  a  particle,  24 ;  -ic  number, 
45 ;  -istic  theory  of  photosynthesis 
of  hydrogen  chloride,  141  ;  Front's 
hypothesis,  151  ;  law  of  whole  num- 
ber atomic  weights,  152  ;  recoil,  154  ; 
chemical  action   by  recoil,   156 ;   im- 

Eact  of  a  particles  with  light  and 
eavy    — ,    163 ;    disruption    of,    22, 


162 ;  of  nitrogen  and  oxygen,  166 ; 
swift  hydrogen  — ,  164  ;  from  nitro- 
gen, 166  ;  nuclear  structure  of,  167  ; 
quantity  of  disruption,  168  ;  gain  in 
energy  by  disruption,  167  ;  multiply 
charged  —  s,  150. 

Barium,  effect  on  color  of  fused  ra- 
dium chloride,  49  ;  —  sulfide,  phos- 
phorescence, 57. 

Beta  particle.  See  also  Penetrating 
rays.  Nature  of,  22  ;  properties,  40  ; 
change  of  valence  by  emission  of, 
42 :  number  of  from  radium,  42 ; 
unit  ionization  by,  42  ;  chemical  ac- 
tion of,  47  ;  coagulation  of  colloids 
by,  47  ;  heat  of  absorption,  65  ;  syn- 
thesis of  hj'drogen  chloride  by,  85, 
119. 

Bleaching  of  dyes,  138, 

Boron,  two  isotopes  of,  153, 

Bromine,  photo-bromination  of  toluene, 
138 ;  of  hexahydrobenzene,  138 ;  of 
hydrogen  not  similar  to  that  of 
chlorine,  142  ;  two  isotopes  of,   152. 

Canal  rays.  See  also  Positive  rays. 
Discovery  of,   148, 

Carbon,  tetrachloride  —  radiochemical 
action  on,  63  ;  dioxide,  decomposition 
by  a  particles,  85,  93,  121  ;  mon- 
oxide, reduction  by  hydrogen  (em- 
anation), 90;  decomposition  by  o 
particles,  97  ;  no  isotopes  of,  153, 

Catalysis,  143  ;  over-emphasis  in  radio- 
chemistry,  19  ;  action  of  a  rays  non- 
catalytic,  59 ;  radiation  theory  of, 
144. 

Chemical  action,  by  o  particles,  73,  92, 
97,  110,  122 ;  by  penetrating  rays, 
47  ;  in  gases  by  electrical  discharge, 
43 ;  of  emanation,  kinetic  equation, 
95,  99  ; ,  of  a  rays,  ther- 
mal theory  of,  115,  116 ;  ionization 
by,  128-9  ;  radiation  theory  of,  142, 
145  ;   by  a  recoil,   156. 

Chemical    effect,    of    penetrating    rays,  , 
47  ;  of  radium  emanation,  65,  72,  89, 
95  ;  of  electrical  discharge  in  gases, 
43.  123  ;  of  recoil  atoms.  156  ;  tables, 
157,  160.     See  also  Chemical  Action. 

Chlorine,  from  radium    (barium)    chlo- 

.  ride,  48  ;  combination  with  hydrogen, 
by  a  rays,  85  ;  by  j8  and  7  rays,  85, 
119  ;  by  X  rays,  129  ;  photochemical, 
118,  132,  141  ;  inhibition  of,  119 ; 
separation  of  isotopes  of,  154. 

Chloroform,  radiochemical  action  on, 
64. 

Collision,  ionisation  by,  43,  124. 

Colloidal,  coagulation  by  j8  and  7  rays, 
47;  coloration  theory,  50, 

Color,  and  luminescence  by  radium,  52  ; 
loss  of  and  thermoluminescence,  53  ; 
change  from  brown  to  violet  by  heat- 
ing, 52,     See  also  Coloration. 


173 


174 


INDEX  OF  SUBJECTS 


Coloration,  of  salts,  47  ;  by  radium,  50  ; 

colloidal  theory  of,  51 ;  of  minerals, 

51,  52  ;  of  glass,  51. 
Corona,  ozonization  by,  81,  125  ;  active 

hydrogen  in,  112. 
Corpuscular  nature  of  a  particle,  21. 
Crystal  structure  by  7  ray  method,  44. 
Curie,  definition  of,  25. 
Cylinder,  average  of  a  particles  in,  83. 

Decay,  constant  (X)  of  radioactive 
substances,  23  ;  of  luminosity  of  zinc 
sulfide,  54. 

Decomposition  table  of  Radium  emana- 
tion. Appendix  A ;  of  radium  salts, 
47  ;  inorganic  by  penetrating  rays, 
63 ;  organic,  64 ;  of  water  by  polo- 
nium, 75 ;  by  radium  solution,  60, 
75,  85  ;  of  hydriodic  acid  by  pene- 
trating rays,  63 ;  of  water  by  em- 
anation, 68,  87,  113,  120;  of  gases 
by  emanation,  85,  93,  97;  of  hj- 
driodic  acid  by  a  rays,  85  ;  of  solid 
salts  by  ^  and  7  rays,  86 ;  of  am- 
monia  by  electrical  discharge,  125 ; 
thermal  of  phosphine,  anomalous, 
145;  of  atoms,  22,  162,  167;  of 
nitrogen  and  oxygen  by  a  rays,  166 ; 
of  nitrogen  pentoxide,  146. 

Dehydration,  of  radium  salts,  49. 

Deposit,  active-rate  of  diffusion,  105 ; 
location  of,  105. 

Diameter,  of  sphere, — influence  on 
chemical  action  produced  by  radium 
emanation,  100. 

Diffraction  of  X  rays  by  crystals,  44. 

Diffusion  of  active  deposit,  105. 

Disintegration,  of  quartz  by  radium 
ravs,  49 ;  of  atoms  by  a  particles, 
162,  166. 

Dyes,  bleaching  of,  138. 

Einstein  photochemical  equivalence, 
132;  tests  of,  133,  136,  146;  excess 
of  chemical  action,  119.  See  also 
Equivalence  and  Photochemistry. 

Electrical,  deflection  of  o  rays,  22 ;  of 
positive  rays,  150  ;  of  swift  hydrogen 
atoms,  165  ;  discharge  in  gases,  37  ; 
discharge,  ozonization  by,  124 ;  de- 
composition of  ammonia  by,  126 ; 
combination  of  hydrogen  and  oxygen 
by,  125 ;  chemical  effect  of,  123 ; 
— charge,  production  by  chemical  ac- 
tion,  128. 

Electron,  -ic  nature  of  /3  particle,  22; 
variable  mass  of,  41 ;  —  theory  of 
photochemical  action,  119  ;  loosening 
of  valence  -s  by  light,  134,  140; 
possibility  of  atomic  disruption  by, 
168.     See  also  Therm-electron. 

Emanation  (radium),  equilibrium  with 
active  deposit,  25  ;  properties  of,  35  ; 
chemical  effect  of,  65,  66 ;  decom- 
position of  water,  ice  and  water 
vapor  by,  69.  87,  120;  action  of  on 
hydrogen,  85 ;  on  oxygen,  72,  85 ; 
determination  of  by  7  radiation,  77  ; 
purification  of,  79 ;  effective  in  re- 
duction of  carbon  monoxide  by  hy- 
drogen, 90 ;  kinetic  equation  for 
action  of  —  on  gases,  95,  99  ;  effect 
of  volume  on  chemical  efficiency  of, 
101 ;  disappearance  of  —  from  spec- 
trum tubes,  127 ;  decay  table.  Ap- 
pendix, Table  A. 

Energy,  radiant,  17 ;  kinetic,  concen- 
tration in  the  a  particle,  22 ;  of 
Ionization,  29;  radiated  by  various 
rays,    42;    utilization,    chemical    of 


penetrating  rays,  01 ;  small  in  photo- 
chemical action,  123  ;  of  a  rays  in 
chemical  action,  122 ;  of  recoil 
atoms,  155  ;  of  swift  hydrogen  atoms, 
163 ;  gain  in  by  artificial  radio- 
activity, 168. 

Enumeration,  of  a  particles,  31,  79  ;  of 
)8  particles,  42. 

Equilibrium,  radioactive,  24 ;  of  am- 
monia (emanation),  72;  of  hydro- 
gen, oxygen,  and  water  (emanation), 
91,  104. 

Equivalence,  ionic-chemical,  75,  82,  85, 
90,  114;  exceptions  to,  117,  120;  of 
ozonization  and  ionization,  80 ; 
photochemical,  132,  133,  138,  146. 

Esters,  radiochemical  formation  and 
decomposition,  63. 

Excess,  of  hydrogen  from  decomposi- 
tion of  water  by  radium,  48  ;  by  em- 
anation, 61  ;  influence  of  —  of  hy- 
drogen or  oxygen  on  rate  of  syn- 
thesis of  water,  107-10  ;  of  chemical 
action  over  ionization,  118  ;  of  ion- 
ization over  chemical  action,  120 ; 
over  theory  of  photochemical  action, 
136,  140. 

Explosion,  ionization  by,  130 ;  infra- 
red radiation  in,  146. 

Faraday's  Law,  applicable  to  decom- 
position of  water  by  polonium,  75  ; 
to  ozonization  by  a  rays,  80 ;  In- 
applicable to  ozone  formation,  124, 
and  ammonia  decomposition  by  elec- 
trical discharge,  126. 

First  order  reaction,  24,  145. 

Fluorine,  simple  element,  153. 

Fumaric  acid,  radiochemical  action  on, 
63,  139. 

Gamma  Rays,  nature,  22 ;  properties, 
44 ;  heat  of  absorption,  65 ;  deter- 
mination of  emanation  by.  77. 

Gas,  -es,  specific  ionization  and  stop- 
ping power  for  a  particles,  32  ;  dis- 
appearance from  discharge  tubes,  39, 
127 ;  evolution  from  radium  salts 
and  solutions,  48 ;  chemical  action 
of  electrical  discharge  in,   43,   123 ; 

—  pipette  (Ramsay),  66;  kinetic 
equation  for  chemical  action  of  em- 
anation on,  95,  99  ;  —  reactions  and 
explosions,   ionization   by,   129,  130: 

—  ions,  variety  of.  81 ;  rate  of 
recombination  of,  117. 

Glass,  coloration  by  radium,  53 ;  ab- 
sorption of  hydrogen  in  under  o 
radiation.  112 ;  thin  —  capillaries 
and  bulbS,  76,  87. 

Half  life  period  of  radioactive  ele- 
ments, 23  ;  relation  to  half  period  of 
chemical  action  by  emanation.  70. 

Heat  evolution,  continuous  from  ra- 
dium, 20  ;  quantity  of  from  radium, 
65  ;  quantity  of  from  a,  i3,  and  7 
rays,  65. 

Helium,  a  particle,  22  ;  accumulation 
from  radioactive  change,  24  ;  simple 
element,  153  ;  —  particles  of  mass, 
3,  167. 

Hydrogen,  excess  of  decomposition  of 
water  by  radium,  48  :  by  emanation, 
80  ;  action  of  emanation  on,  61,  72, 
85,  111  :  combination  with  oxygen, 
72,  85,  89,  97.  99,  101,  107  ;  in  elec- 
trical discharge,  125 ;  —  -oxygen 
equilibrium  (emanation),  91,  104; 
influence  of  excess  of  on  synthesis 


INDEX   OF   SUBJECTS 


175 


of  water,  109  ;  —  chloride,  synthesis 
of  by  a  rays,  85.  135,  137,  141  ;  by 
/3  and  y  rays,  85,  119  ;  by  X  rays, 
129;  by  light,  128,  132;  —  iodide, 
photolysis  of,  134;  decomposition  of 
by  a  rays,  86  ;  —  pero^de,  syn- 
thesis, 62 ;  energy  utilization  of 
penetrating  rays  in  synthesis  of.  61 ; 
photolysis  of,  188,  201  ;  —  .sulfide, 
decomposition  by  emanation,  93, 
121  ;  inhibition  of  photochemical  ac- 
tion of  —  and  chlorine,  118 ;  tri- 
and  mono-atomic,  active,  112 ;  re- 
duction of  carbon  monoxide  by  — 
(emanation).  90;  absorption  in  glass 
under  a  radiation,  112  ;  simple  ele- 
ment, 153 ;  swift  —  atoms,  from 
hydrogen,    164 ;    from   nitrogen,    167. 

Ice,  decomposition  by  a  rays,  88,  120. 

Increment  of  internal  energy  (chem- 
ical), 143. 

Infra-red,  radiation  in  chemical  action, 
142,  145  ;  —  absorption  of  methyl 
acetate,  144. 

Inhibition,  of  photochemical  interac- 
tion of  hydrogen  and  chlorine,  119  ; 
general  by  oxygen  of  photo-reactions, 
135. 

Interference,  of  X  rays  in  crystals,  44. 

Iodide,  photolysis  of  hydrogen  — ,  134  ; 
decomposition  of  -s  by  jS  and  7  rays, 
62. 

Iodoform,  phot-oxidation  of,  138. 

Ionization.  See  also  Ions.  —  by  o 
particle,  27 ;  curve  of,  30,  136 ;  by 
collision,  39,  43,  124 ;  Townsend's 
formula,  43 ;  —  formula  of  Duane 
and  Laborde,  66,  83,  85  ;  by  therm- 
electrons,  43  ;  specific  —  of  gases  by 
a  particle,  92  :  —  theory  of  chemical 
action,    74,    124  ;    calculation   of,    78, 

83 ;    ,    evaluation    of    M/N, 

103  ;  unit  —  by  a  and  jS  rays,  29,  42, 
80,  116  ;  —  by  chemical  action,  128, 
130  ;  by  recoil,  155. 

Ions,  energy  to  produce  one  pair  of, 
29 ;  ionic-chemical  equivalence.  75, 
115,  140  ;  cluster  — ,  81 ;  variety  of 
gas  — ,  81,  150 ;  rate  of  recombina- 
tion of  gas  — ,  117  ;  absence  of  in 
chemical  action,  128.  See  also  Ion- 
ization. 

Isotopes,  analysis  of  by  positive  rays, 
149 ;  of  neon,  151  ;  of  various  ele- 
ments, 152  ;  separation  of,  151,  153  ; 
of  helium,  167 ;  by  atomic  disrup- 
tion. 168  :  radioactive  — ,  Appendix, 
Table  B,  172. 

Kinetic,  -s  of  radioactive  transforma- 
tion, 23 ;  energy  of  a  particle.  26 ; 
-s  of  gas  reactions  (radiochemical), 
94  ;  equation  of,  95  ;  application,  99  ; 
—  equations,  107  ;  -s  of  water  svn- 
thesis  (by  emanation),  100.  107; 
chemical  -s  and  radiation,  147  ;  en- 
ergy of  recoil  atoms,  155. 

Krypton,  six  isotopes  of,  153. 

Lambda,  decay  constant,  definition  of, 
23. 

Lead,  attempt  to  separate  isotopes  of, 
154. 

Lenard  rays,  ozonization  by,  80,  123. 
See   also  Electrons. 

Levulose,  photolysis  of,  134. 

Luminescence,  blue  of  fused  radium 
salts,  50  ;  and  color  by  radium,  51, 
53  :  active  centers  of.  54  ;  decay,  54, 
and  recovery,  of  in  zinc  sulfide,  54. 


Magnetic  deflection,  of  a  particles,  22  ; 
of  j3  particles,  41 ;  of  positive  rays, 
148  ;  of  swift  hydrogen  atoms,  167. 

Maleic  acid,  radiochemical  action  on, 
63,   139. 

Manometric  measurement  of  the  ve- 
locity of  gas  reactions,  65. 

Mass,  of  electron  variable,  41 ;  — 
spectrograph,  149  ;  —  spectra,  151 ; 
of  swift  particles  from  hydrogen, 
nitrogen  and  oxygen  atoms,  167. 

Mercury,  effect  of  hydrogen  and  oxygen 
on,  in  presence  of  radium  emanation, 
111  ;  isotopes  of,  153 ;  separation, 
154. 

Meso-thorium,  life  period,  55 ;  in  lu- 
minous material,  55. 

Mica,  pleochroic  rings  in,  52. 

Minerals,  coloration  of,  50,  52  ;  range 
of  a  rays  in,  51  ;  pleochroic  rings 
and  geological  age  of,  51 ;  photo- 
electric effect  in,   50,  52. 

Molecules,  active,  143. 

Monatomic,  character  of  radioactive 
transformations,  23,  25 ;  hydrogen, 
112. 

Neon,  isotopes  of,  151;  triad  (?),  151, 
153. 

Nitro-benzaldehyde,  radiochemical  con- 
version to  acid,  63. 

Nitrogen,  simple  element,  153  ;  disrup- 
tion of,  166  ;  swift  hydrogen  atoms 
from,  167  ;  swift  helium  atoms  from, 
167  ;  decomposition  of  nitrous  oxide 
by  a  rays,  85,  93;  of  —  pentoxide, 
147. 

Number,  of  a,  31,  j3,  41,  and  7  rays 
from  radium,  42  ;  atomic  — ,  45. 

Order  of  reaction,  first,  24. 

Oxygen.  See  also  Ozone,  Ozonization, 
and  Phot-oxidation.  Combination 
with  hydrogen,  by  emanation,  72,  85, 
97,  99,  101,  107 ;  by  electrical  dis- 
charge, 125  ;  effect  of  emanation  on 
—  in  the  presence  of  mercury.  111 ; 
effect  of  excess  of  —  in  the  syn- 
thesis of  water  by  emanation,  110  ; 
inhibition  by,  135 ;  simple  element, 
153  ;  disruption  and  swift  particles 
from,  165. 

Ozone.  See  also  Ozonization.  Forma- 
tion by  a  rays,  80  ;  photolysis.  1,36. 

Ozonization,  by  a  rays,  76,  80,  85,  123  ; 
bv  Lenard  rays,  80,  123  ;  in  corona, 
124  ;  photochemical,  134  ;  theory  of, 
123. 

Path,  average  of  a  rays,  calculation, 
82  ;  influence  on  chemical  activity  of 
radium  emanation,   100. 

Penetrating  rays,  from  radium,  34 ; 
chemical  action  of,  47,  61.  112  ;  en- 
ergy utilization  in  synthesis  of  hy- 
drogen peroxide,  61  ;  decomposition 
of  hydriodic  acid,  63  ;  of  water  by, 
114  ;  synthesis  of  hydrogen  chloride 
by,  85,  119. 

Phosgene,  photo-synthesis  of,  138. 

Phosphine,  anomalous  decomposition 
of,  145. 

Phosphorescent,  alkaline  earth  sul- 
fides, 57  ;  zinc  sulfide,  54  ;  willemite, 
57. 

Phosphorus,  simple  element,  153. 

Photochemical,  reduction  of  ferrous 
sulfate,  63  ;  small  energy  utilization 
in  —  action,  123 ;  —  equivalence, 
132,     138,    145 ;     comparison     with 


176 


INDEX   OF   SUBJECTS 


ionic-chemical       equivalence,       140 ; 

—  interaction  of  hydrogen  and 
chlorine,  136:  inhibition  of,  118; 
synthesis  of  phosgene,  138  ;  ozoniza- 
tion,  134 ;  bromination  of  toluene, 
138  ;  of  hexahydrobenzene,  139  ;  the- 
ory of  —  action,  140  ;  decomposition 
of  nitrogen  pentoxide,  147.  See  also 
Photochemistry  and  Photolysis. 

Photochemistry,  texts  of,  7 ;  relation 
of  to  radiochemistry,  18  ;  comparison 
with  a  ray  effects,  57  ;  —  of  hydro- 
gen-chlorine reaction,  118,  132 ;  of 
primary,  134,  and  secondary  light 
reactions,  137. 

Photo-electric  effect  and  coloration  of 
minerals,   50,  52. 

Photolysis,  of  ammonia,  hydriodic  acid 
gas,  levulose,  ozone,  134  ;  of  hydro- 
gen peroxide,  ozone,  136 ;  of  hydro- 
gen bromide,  140. 

Phot-oxidation,  of  quinine,  137 ;  of 
iodoform   and  hydrogen   iodide,   137. 

Pleochroic  rings  in  mica,  52. 

Polonium,  a  particles  from,  36  ;  decom- 
position of  water  by,  75. 

Positive,    charge    of    a    particle,    22 ; 

—  rays,  148 ;  analysis  by.  149 ; 
method  of,  149 ;  magnetic  deflection 
of,  148  ;  isotopes  discovered  by,  151. 

Potassium,  radioactivity  of,  24 ;  — 
iodide  (acid),  decomposition  by  o 
rays,  86. 

Primary  light  reactions,  133  ;  Table  of, 
134. 

Prout's  Hypothesis,  renewed  impor- 
tance of,  151. 

Qualitative  and  quantitative  radio- 
chemical effects,  46. 

Quantum  theory,  132,  136. 

Quartz,  disintegration  by  radium  rays, 
49. 

Radiation,  forms  of,  18,  21 ;  continu- 
ous emission  by  radium,  20 ;  emana- 
tion as  source  of,  65 ;  theory  of 
chemical  action  of,  142 ;  —  theory 
of  catalysis,  144  ;  distribution  of  — 
in    time    and    space,    37;    infra-red 

—  in  explosions,  146.  See  also  o. 
P,  7,  positive  and  Lenard  rays  and 
recoil  atoms. 

Radioactivity,  theory  of,  20,  21 ;  phe- 
nomena of,  21 ;  series  of,  23  ;  —  of 
potassium  and  rubidium,  24  ;  radio- 
active    equilibrium,     25 ;     standards 

and  units  of,  25  ;  ,  isotopes 

resulting  from.  Appendix,  Table  B, 
172  ;  "artificial"  — ,  166,  168. 

Radiochemistry,  definition,  17  :  relation 
to  photochemistry,  18  ;  problems  of, 
74. 

Radio-thorium,  life  of  and  use  in  lu- 
minous material,  55. 

Radium.  See  also  Emanation  and 
Radiation.  Discovery  of  radiations, 
20;  equilibrium  with  emanation.  25; 

—  family,  Table  I,  28 ;  standards, 
26 ;  number  of  a,  31,  /3,  42,  and  y 
rays  from,  42  ;  —  salts  and  solution, 
gas  evolution  from,  47  ;  precautions 
In  sealing  —  in  tubes,  48 ;  —  lu- 
minous paint,  54 ;  recovery  of  lu- 
minosity in,  54 ;  disintegration  of 
quartz  by  — ,  49  ;  coloration  l)y,  50  ; 
l)lue  luminescence  of  fused  —  salts, 
50 ;  decomposition  of  water  in  — 
pplVtloR,  59,  75,  85, 


Radium  A,  B,  C,  D,  E,  F,  properties, 
36  ;  heat  from   Ra  A  and   Ha  C,  65. 

Range,  of  a  particle,  27  ;  end  of,  27  ; 
in  minerals,  51  ;  radiometric  deter- 
mination of,  77  ;  of  swift  atoms,  163. 

Recoil,  from  a  particles,  23,  154;  en- 
ergy and  velocity  of  —  atoms,  155  ; 
chemical  action  of,  156. 

Reflection  of  X  rays  by  crystals,  44. 

Roentgen   rays.      See  X   rays. 

Rubidium,  radioactivity  of,  24. 

Salts,  coloration  of  by  radiation,  47  ; 
of  radium,  gas  evolution  from,  48 ; 
decomposition  of  in  solution,  03  ;  in 
solid  state,  86. 

Saturation  current,  as  a  measure  of 
ionization,  37. 

Scattering,  of  /3  particles,  41  ;  of  a 
particles,    163. 

Scintillation,  of  zinc  sulflde  by  a  rays, 
53  ;  by  swift  particles  from  hydro- 
gen, 164  ;  nitrogen  and  oxygen,  163, 
166. 

Secondary  light  reactions,  132;  table 
of,  136. 

Separation  of  isotopes,  154. 

Sidot's  blende,  54.  See  also  Zinc  Sul- 
flde. 

Silent  discharge,  124.  See  also  Elec- 
trical discharge. 

Silicon,  two   isotopes  of,  153. 

Solids,  chemical  effect  of  radiation  on, 
86,  121. 

Solution,  radium-gas  evolution  from, 
48 ;   decomposition   of  water   in,   86. 

Sphere,  average  path  of  a  particles  in, 
82  ;  influence  of  size  on  chemical  ac- 
tion of  emanation,  100. 

Standard,    radium,   26. 

Stopping  power  toward  a  particles,  32, 
33  ;  Table  II,  33. 

Sugar  inversion,  radiochemical,  63. 

Sulflde,  alltaline- earth,  phosphorescent, 
57  ;  zinc,  phosphorescent,  54. 

Sulfur,   simple   element,   153. 

Synthesis,  of  hydrogen  chloride  by  a 
rays,  85  ;  by  ^  and  y  rays,  119  ;  by 
X  rays,  128;  by  light,  118,  136;  of 
water,  ammonia,  and  hydrogen  bro- 
mide by  emanation.  72.  85,  89,  97, 
99,  116;  of  water  by  electrical  dis- 
charge, 125. 

Temperature  coeflicient,  of  radiochem- 
ical action  on  water,  61  ;  on  potas- 
sium iodide,  63  ;  on  hydrogen  sulflde. 
ammonia,  and  nitrous  oxide,  93  ;  of 
reaction  velocity,  143. 

Theta  ((?),  average  life  period,  deflni- 
tion,  24. 

Therm-electrons,   ionization   by,   43. 

Thermoluminescence,  and  loss  of  color, 
52. 

Thorium  series,  23.  See  also  Meso- 
and  Radio-thorium. 

Toluene,  radiochemical  action  on,  64  ; 
photo-bromination   of,    138. 

Tube,  X  ray  of  Coolldge,  40,  45;  thin, 
o  ray-penetrable,  76,   80. 

Ultra-violet  light,  chemical  effects  of, 
68. 

Unit,  -s  of  radioactivity.  26 ;  —  Ioniza- 
tion by  a  particles,  29  ;  by  )3  and  y 
rays,  42. 

Uranium,  series,  28;  Table  I,  28; 
equilibrium  in,  24. 


INDEX   OF   SUBJECTS 


177 


Valence,  change  of  by  emission  of  a 
and  /8  particles,  42 ;  —  electrons, 
loosening  of  by  light,  134,  140. 

Velocity,  equation  of  a  particle,  31  ;  of 

gas  reactions  by  manonietric 

method,  65  ;  of  diffusion  of  active 
deposit,  105  ;  abnormal  of  phosphine 
decomposition,  144;  of  recoil  atoms, 
155  ;  of  swift  hydrogen  atoms,   163. 

Water,  excess  hydrogen  from  decom- 
position of  by  radium,  48  ;  by  emana- 
tion, 61 ;  synthesis,  72  ;  decomposi- 
tion by  emanation,  69,  89,  113,  120  ; 
by  electrical  discharge,  125  ;  by  po- 
lonium, 75 ;  by  radium  in  solution, 
59,  75  ;  synthesis  of  by  emanation, 
89,  97,  99,  117  ;  —  vapor,  decomposi- 
tion by  emanation,  87,  120  ;  equilib- 


rium    with     hydrogen     and     oxygen 
(emanation),  91,  104.     See  also  Ice. 
Willemite,  phosphorescence  of,  56. 

X  rays,  discovery,  20,  44 ;  properties, 
44  ;  ionization  by  shock  in  —  tube, 
39  ;  interference,  diffraction  and  re- 
flection by  crystals,  44  ;  structure  of 
crystals  by,  44  ;  —  tube  of  Coolidge, 
40,  45  ;  characteristic,  synthesis  of 
hydrogen  chloride  by,  129. 

Xenon,  absorption  of  by  electrodes 
(chemical?),  127;  five  isotopes  of, 
153. 

Zinc  sulfide,  pure,  non-luminescent,  70; 
decay  of  luminosity  in,  54  ;  recovery 
of  luminosity  in,  54. 


INDEX  OF  AUTHORS 


Anderegg,    F.    O.,    ozonization    In    the 

corona,  125. 
Arrhenius,  S.,  active  molecules,  143. 
Aston,    F.    W.,    positive    ray    analysis, 

149  ;  isotopes  of  neon,  151 ;  of  other 

elements,  152. 
Aston,  F.  W.     See  Lindemann,  F.  A., 

151. 

V.  Bahr,  B.,  photolysis  of  ozone, 
137. 

Baly,  E.  C.  C,  Einstein's  Photochem- 
ical Law,  145. 

Bancroft,  W,  D.,  colloidal  coloration, 
50. 

Barkla,  C.  G.,  characteristic  X  radia- 
tion, 45. 

Baslcerville,  C.     See  Kunz,  G.  P.,  57. 

Becquerel.  H.,  discovery  of  Becquorel 
rays,  20,  44 ;  chemical  action  of  /3 
and  7  rays,  47. 

Benrath,  A.,   photochemistry,  7. 

Bergwitz,  K.,  decomposition  of  water 
by  polonium,  75. 

Berth  clot,  D.,  and  Gaudochon,  H.,  pho- 
tolysis of  levulose,  134. 

Bhandarkar,  D.  S.  See  Trautz,  M., 
145. 

Bigelow,  S.  L.,  first  order  reactions,  24  ; 
Front's  Hypothesis,  152. 

Bloch,  Ij.,  ionization  by  chemical  ac- 
tion, 129. 

Bodenstein,  M.,  synthesis  of  hydrogen 
chloride  by  a  rays,  85,  119  ;  photo- 
chemical equivalence,  132 :  primary 
light  reactions,  134  ;  secondary  light 
reactions,  137  :  photolysis  of  hydro- 
gen iodide,  134 ;  theory  of  photo- 
chemical action,  134.  140. 

Bodenstein,  M.,  and  Dux.  W.,  photo- 
synthesis of  hydrogen  chloride,  135, 
137. 

Bodiander,  G.     See  Rungo.  G.,  CO. 

Bohr,  N.,  atomic  model,  27. 

Boll,  M.,  photochemical   action,   137. 

Boll,  M..  and  Job.  P.,  photo-hydrolysis 
of  chloroplatinic  acid,   137. 

Bragg,  W.  n.,  radioactivity,  8  ;  kinetic 
energy  of  a  particle,  20 ;  ionization 
curve  of  a  particle,  30,  103 ;  stop- 
ping power  for  a  particle,  32,  33 : 
first  calculation  of  ionic-chemical 
equivalence,  75 ;  specific  ionization 
of  gases  by  o  particles,  92. 

Bragg,  W.  II.,  and  Bragg,  W.  L.,  crys- 
tal structure,  44. 

Bragg,  W.  H.,  and  Klooman,  R.  D., 
Identity  of  a  particles,  20. 

Bragg,  W.  L.,  reflection  of  X  rays  by 
crystals,  44. 

Bragg.  W.  L.     See  Bragg.  W.  IT.,  44. 

Brizard,  L.     See  Broglle.  Af..  130. 

Broglie.  M..  and  Brizard,  li..  absence 
of  ionization  by  chemical  action, 
130. 


Bronsted,  J.  N.,  and  v.  Hevesy,  G., 
separation  of  isotopes  of  mercury, 
154. 

Brooks,  IT.  T.,  recoil  from  o  par- 
ticles, 154. 

Bruner,  L.,  and  Czernicki,  S.,  photo- 
bromination  of  toluene,  138. 

Bunsen,  R.,  and  Roscoe.  IT.  E.,  photo- 
synthesis of  hydrogen  chloride, 
118. 

Callow,  R.  H.,  and  Lewis,  W.  M.  McC, 
radiation  in  chemical  action,  142. 

Cameron.  A.  T.,  and  Ramsay,  W.,  chem- 
ical effects  of  emanation,  (50 ;  ap- 
paratus, 66-9  ;  synthesis  of  water  by 
emanation,  85,  97  ;  decomposition  of 
ammonia,  hydrogen  chloride,  and 
carbon  dioxide  by  emanation,  85 ; 
synthesis  of  ammonia  by  emanation, 
85,  98 ;  decomposition  of  carbon 
monoxide  by  emanation,  97. 

Campbell,  N.  R.,  and  Ryde,  .T.  W.  H., 
disappearance  of  gas  in  electrical 
discharge,  128. 

Campbell,  N.  R.,  and  Wood,  A.,  radio- 
activity of  potassium  and  rubidium, 
24. 

Chapman,  D.  L.,  theory  of  isotopic 
separation,  154. 

Chapman,  D.  L.,  and  Gee,  F.  IT.,  photo- 
synthesis of  phosgene,  138. 

Chapman,  D.  L.,  and  MacMahon,  P.  S., 
inhibition  of  photochemical  action, 
119. 

Coblentz.  W.  W.,  infra-red  absorption 
of  methyl  acetate,  144. 

Collie,  J.  N.,  absorption  of  xenon 
(chemical?),  127. 

Coolidge,  W.  D.,  X  ray  tube,  40,  45. 

Core,  A.  F.,  theory  of  isotopic  separa- 
tion, 154. 

Creighton,  IT.  J.  M.,  and  McKenzie,  A. 
G.,  decomposition  of  hydriodic  acid 
by  penetrating  rays.  03. 

Curie,  P.,  and  Curie,  Mme.  P.,  colora- 
tion of  glass,  47. 

Curie,  P..  and  Debierne,  A.,  gas  evolved 
by  radium  salts  and  solutions.  48. 

Curie.  P..  and  Laborde,  A.,  theory  of 
radioactivity.  20. 

Curie,  Mme.  P.,  radioactivity.  8,  24 ; 
corpuscular  nature  of  a  particle,  22  ; 
radium  standards.  20,  59 ;  lumines- 
cence and  color,  51  ;  energy  of  pene- 
trating rays  chemically  utilized,  61 ; 
ionic  chemical  equivalence.  75. 

Curie,  Mme.  P.     See  Curie,  P.,  47. 

Czernicki,  S.     See  Bruner,  L.,  138. 

Daniels,  F.,  and  Johnston,  E.  II.,  de- 
composition of  nitrogen  pentoxide, 
147. 

Darwin,  C.  G.,  X  radiation,  45  ;  scat- 
tering of  a  particles,  163. 


178 


INDEX  OF  AUTHORS 


179 


David,  W.  T.,  infra-red  radiation  in 
chemical  reaction,  146. 

Davies,  J.  H.,  decomposition  of  am- 
monia by  electrical  discharge,  126. 

Davis,  C.  W.,  pure  zinc  sulfide,  non- 
luminous,  56. 

Debieme,  A.,  excess  of  hydrogen  in  de- 
composition of  water,  48;  decom- 
position of  radium  solution,  S5  ;  dif- 
fusion of  active  deposit,  105  ;  de- 
composition of  water  by  penetrating 
rays,  114  ;  thermal  theory  of  a  ray 
chemical  effect,   116. 

Debierne,  A.     See  Curie,  P.,  48. 

Doelter,  C,  coloration  of  minerals  by 
radium,  50. 

Draper,  J.  W.,  photochemical  action, 
118. 

Duane,  W.,  end  of  range  of  a  particle, 
27  ;  thin  a  ray  bulbs,  76. 

Duane,  W.,  and  Scheuer,  O.,  decom- 
position of  water  by  emanation,  60, 
86  ;  excess  hydrogen  from,  61  ;  extra- 
polation of  ionization  by  emanation, 
84  ;  decomposition  of  water,  ice,  and 
water  vapor,  85-9,  120. 

Duane,  W.,  and  Hu,  K.-P.,  X  radia- 
tion, 45. 

Duane,  W.,  and  Laborde,  A.,  ionization 
formula,  66,  84.  85,  86. 

Duane,  W.,  and  Shimizu,  T.,  X  radia- 
tion,  45. 

Duane,  W.,  and  Wendt,  G.  L.,  active 
hydrogen,  112. 

Dux,  W.     See  Bodenstein,  M.,  135,  137. 

Einstein,  A.,  photochemical  equivalence 
law,  132. 

Fajans.  K..  change  of  valence  by  a  or 
$  radiation.  42  :  radioactive  isotopes, 
Appendix,  Table  B. 

Falckenberg,  G.,  decomposition  of  am- 
monia by  electrical  discharge,  126. 

Fall?,  K.  G.,  first  order  reactions,  24. 

Flamm,  L.,  and  Mache,  H.,  calculation 
of   ionization    by   emanation,    83. 

Fletcher,  A.  L.     See  Joly,  J.,  52. 

Fletcher,  H.     See  Millikan,   R.  A..  42. 

Forbes,  G.  S,     See  Luther,  R.,  134. 

Friedrich,  W.,  Knipping,  P.,  and  Laue, 
M.,  crystal  diffraction,  44. 

Fulcher.  G.  S..  atomic  disruption  and 
artificial  radioactivity,  166,  168. 

Gaudechon,  H.     See  Berthelot,  D.,  134. 

Gee,  F.  H.     See  Chapman.  D.  L.,  138. 

Geiger,  H.,  ionization  curve  of  o  par- 
ticle, 30 :  velocity  equation  of  a 
particle,  31. 

Geiger,  IT.     See  Malcower,  W.,  77. 

Geiger,  H.,  and  Marsden,  E.,  scatter- 
ing of  a  particles,  163. 

Geiger,  H.  See  Rutherford,  E.  E.,  22, 
36. 

Giesel,  F.,  coloration  of  salts,  47. 

Goldberg,  B.     See  Luther,  R.,  135. 

Goldstein,  E.,  coloration  by  cathode 
rays,  51 ;  discovery  of  canal  rays, 
148. 

Gottschalk.  V.  H.  See  Millikan,  R.  A., 
29.  81,  116. 

Griffith.  R.  O.,  Lamble,  A.,  and  Lewis. 
W.  C.  McC,  radiation  in  chemical 
action,  142. 

Griffith,  H.  O..  and  Lewis,  W.  C.  McC, 
radiation  in  chemical  action,  142. 

Ilaber,  F.,  and  Just,  G.,  ionization  by 
chemical  action,  129, 


Hahn,  O.,  recoil  from  a  particle,   154. 

Hall,  N.  F.     See  Richards,  T.  W.,  154. 

Harkins,  W.  D.,  separation  of  isotopes 
of  chlorine,  154. 

Hartley,  H.     See  Merton,  T.  R.,  154. 

Haselfoot,  E.  E.,  and  Kirkby,  P.  J., 
ionization   in   gas   explosions,    130. 

Henri,  V.,  and  Wurmser,  R.,  photo- 
hydrolysis  of  acetone,  137,  145  ;  pho- 
tolysis of  hydrogen  peroxide,  137. 

Hess,  V.  F.,  and  Lawson,  R.  W.,  num- 
ber of  )3  particles  from  radium,  42  ; 
of  a  particles,  79. 

Hess,  V.  F.     See  Meyer,  S.,  65. 

V.  Hevesy,  G.,  change  of  valence  by  o 
or  i8  radiation,  42. 

V.  Hevesy,  G,  See  Bronsted,  J.  N., 
154. 

Higgins,  W.  F.  See  Patterson,  C.  C, 
54. 

Honigschmid,  O.,  radium  standards, 
26  ;  coloration  of  radium  salts,  48  ; 
disintegration  of  quartz  by  radium 
rays,  49 ;  blue  luminescence  of  ra- 
dium salts,  50. 

Horton,  F.,  ionization  by  therm-elec- 
trons, 43. 

Hu,  K.-W.     See  Duane,  W.,  45. 

Hull,  A.  W.,  crystal  structure  by  X 
rays,  45. 

Job,  P.     See  Boll,  M.,  137. 

Johnston,  E.  H.     See  Daniels,  F.,  147. 

Joly,   J.,  range  of  a  rays  in  minerals, 

52 ;   pleochroic   rings  and   geological 

age,  52. 
Jorissen,    W.    P.,    and    Ringer,    W.    E., 

synthesis  of  hydrogen  chloride  by  $ 

and  7  rays,  47,  85,  119. 
Jorissen,  W,  P.,  and  Woudstra,  H.  W., 

coagulation  of  colloids  by  iS  rays,  47. 
Just,  G.     See  Haber,  F.,  129. 

Kabakjian,  D.  H.,  theory  of  ozoniza- 
tlon  by  electrical  discharge,  124. 

Kabakjian,  D.  H.     See  Karrer,  E.,  49. 

Kalian,  A.,  energy  utilization  of  pene- 
trating rays  in  chemical  action,  61 ; 
decomposition  of  hydrogen  peroxide 
by  penetrating  rays,  62  ;  of  alkaline 
halides,  62  ;  of  organic  and  inorganic 
substances,  63-4. 

Karrer,  E.,  and  Kabakjian,  D.  H.,  blue 
luminescence  of  radium   salts,   49. 

Kaufmann,  W.,  mass  of  electron,  41, 

Kelly,  M.  J.  See  Millikan,  R.  A.,  29, 
81,  116. 

Kernbaum,  M.,  formation  of  hydrogen 

geroxide  by  radium  48,  60 ;  excess 
ydrogen  in  decomposition  of  water, 
60. 

Kirkby,  P.  J.,  chemical  action  in  gases 
by  electrical  discharge,  43,  125. 

Kirkby,  P.  J.  See  Haselfoot,  E.  E., 
130. 

Kirkby,  P.  J.,  and  Marsh,  J.  E.,  ioniza- 
tion in  explosive  reactions,  130. 

Kistiakowski,  W.,  bleaching  of  dyes, 
137. 

Klatt,  V.     See  Lenard,  P.,  57. 

Kleeman,  R.  D.,  specific  ionization  of 
gases  by  a  particles,  92. 

Kleeman.  R.  D.     See  Bragg,  W.  H.,  26. 

Kolowrat,  L.,  table  of  decay  of  emana- 
tion, Appendix,  Table  A,  170. 

Knipping,  P.     See  Friedrich,  W.,  44. 

Kriiger,  F.,  ozonization  by  Lenard  rays, 
80,  124  ;  radiation  theory  In  electro- 
chemistry, 144. 


180 


INDEX  OF  AUTHORS 


Kiimniell,  G.,  ionization  in  the  photo- 
chomioal  svnthosis  of  hydrogen 
cblnrUlf.   12S. 

Kummorer.   L.      See  Weigert,   W.,   134. 

Kunz,  G.  F.,  and  Baskerville,  C,  radio- 
luminescence  of  gems,  57. 

Kunz,  J.     See  Rideal,  E.  K.,  81,  125. 

Laborde,  A.     See  Curie,  P.,  20. 

Laborde,  A.  See  Duane,  W.,  66,  84, 
85,  86. 

Larable,  A.,  and  Lewis,  W.  C.  McC, 
radiation  in  chemical  action,  142. 

Landauer,  S.  See  Wendt,  G.  L.,  81, 
112. 

Langevin,  P.,  rate  of  recombination  of 
gaseous  ions,   117. 

Langrauir,  I.,  monatomic  hydrogen, 
112  ;  arrangement  of  molecules  at  an 
Interface,  145  ;  radiation  hypothesis, 
146. 

Lantsberry,  W.  C.  See  Marsden,  E., 
164. 

Laue,   W.,  interference  of  X  rays,  44. 

Laue,  W.     See  Friedrich,  W.,  44. 

Lawson,  R.  W.  See  Hess,  V.  F.,  42, 
79. 

Learning,  T.  H.,  Schlundt,  H.,  and  Un- 
derwood, J.  E,,  application  of  the 
Duane  and  Laborde  ionization  for- 
mula, 66. 

Le  Blanc.  M.,  ionic-chemical  equiva- 
lence, 75  ;  decomposition  of  ammonia 
by  electrical  discharge,  126. 

Le  Blanc,  Rf.,  and  Vollmer,  M.,  syn- 
thesis of  hydrogen  chloride  by  X 
rays,  128. 

Lenard,  P.,  and  Klatt,  V.,  phosphores- 
cent alkaline  earth  sulfides,  57. 

Lewis.  W.  C.  McC,  photochemical 
equivalence,  133 ;  radiation  theory 
of  chemical  action,  142  ;  anomaly  of 
phosphine  decomposition,  145. 

Lewis,  W.  C.  McC.  See  Callow,  R.  H., 
142. 

Lewis,  W.  C.  McC.  See  Griffith,  R.  O., 
142. 

Lewis,  W.  C.  McC.  See  Griffith,  R.  O., 
and  Lamble,  A.,  142.  • 

Lewis,  W.  C.  McC.  See  Lamble,  A., 
142. 

Lind,  S.  C,  loss  of  color  and  thermo- 
luminescence,  52 ;  synthesis  of  wa- 
ter by  emanation,  71,  85 ;  decom- 
position of  ammonia  by  one  o  par- 
ticle, 73  ;  ozonization  by  o  rays,  76, 
85,  124;  thin  a  ray  bulbs,  76;  ra- 
diometric determination  of  range  of 
a  ray,  78 ;  theory  of  ozone  forma- 
tion, 81 ;  average  path  of  a  ray,  82  ; 
synthesis  and  decomposition  of  hy- 
drogen bromide  by  emanation.  86 ; 
decomposition  of  hydriodic  acid  and 
of  solid  salts,  86 ;  equilibrium  of 
hydrogen  and  oxygen  (emanation), 
91,  104  ;  kinetic  equation  for  chem- 
ical action  of  emanation  on  gases. 
95  ;  application  of,  99  ;  influence  of 
size  of  sphere  on  rate  of  water  syn- 
thesis (emanation),  101;  location  of 
active  deposit,  105  ;  excess  of  com- 
ponents In  water  synthesis  (emana- 
tion), 107;  action  of  emanation  on 
pure  hydrogen  or  oxygen.  Ill  ;  ionic- 
chemical  equivalence,  115  ;  chemical 
action  by  recoil  atoms  of  a  particles, 
156-160. 

Lindemann,  F.  A.,  radiation  hypo- 
thesis, 146 :  theory  of  separation  of 
Jsotopes,  J5l. 


Lindemann,  F.  A.,  and  Aston,  F.  W., 
separation  of  isotopes  of  neon,  151. 

lioeb,  L.  B.,  cluster  ions,  81. 

Lunn,  A.  C,  average  path  of  a  rays, 
82. 

Luther,  R.,  photography  and  photo- 
chemistry, 18. 

Luther,  R.,  and  Forbes,  G.  S.,  phot- 
oxidation  of  quinine.  134. 

Luther,  K.,  and  Goldberg,  E.,  inhibi- 
tion, 135. 

Luther,  R.,  and  Weigert,  F.,  photo- 
chemical polymerization  of  anthra- 
cene, 134. 

Mache,  H.     See  Flamm.  L.,  83. 

MacMahon,  P.  S.  See  Chapman,  D.  L., 
119. 

Makower,  W.,  and  Geiger,  H.,  y  ray 
determination  of  emanation.  77. 

Makower,  W.     See  Russ,  S.,  154. 

Marcelin,  R.,  increment  of  Internal 
energy,  143. 

Marsden,  E..  decay  of  luminosity  of 
zinc   sulfide,  54. 

Marsden,  E.     See  Geiger,  XL,  163. 

Marsden,  E.,  and  Lantsberry,  W.  C, 
long  range  hydrogen  atoms,  164. 

Marsh,  J.  E.     See  Kirkl)y,  P.  J.,  130. 

McKenzie,  A.  G.  See  Creighton,  II.  J. 
M..  63. 

McKlung,  R.  K.,  rate  of  recombination 
of  gaseous  Ions,  117. 

Meitner,  Frl.  L.,  life  of  meso-thorlum, 
55. 

Mellor,  J.  W.,  chemical  kinetic  calcula- 
tions, 108. 

Merton.  T.  R..  and  Hartley,  H.,  theory 
of  separation  of  isotopes,  154. 

Meyer,  S.,  and  Hess,  V.  F.,  disintegra- 
tion of  quartz  by  radium  rays,  49  ; 
heat  evolution  of  radium,  65. 

Meyer.  S.,  and  Przibram,  K.,  photo- 
electric effect  and  coloration  of  min- 
erals, 50,  51. 

Meyer.  S.,  and  V.  Schweidler,  E.,  radio- 
activity, 8,  24 ;  radium  standards, 
26 :  energy  and  velocity  of  recoil 
atoms,  155. 

Millikan,  R.  A.,  and  Fletcher,  H.,  ion- 
izntion  by  /8  particles,  42. 

Millikan,  R.  A..  Gottschalk,  V.  H.,  and 
Kelly,  M.  J.,  Ionization  by  a  par- 
ticles. 29,  81,  116. 

Moore.  R.  B.,  use  of  meso-thorlum  In 
luminous  paints,  55. 

Moseley,  H.  G.  J.,  number  of  j8  par- 
ticles, 42  ;  atomic  numbers,  44. 

Mof^.eley.  H.  G.  J.,  and  Robinson.  H., 
number  of  7  rays  from  radium,  42. 

Nernst,  W..  photochemical  equivalence, 
133.    136;    mechanism   of  photo-syn- ' 
thesis  of  hydrogen  chloride,  141. 

Ostwald,  W.,  photochemical  researches 
of  Bunsen  and  Roscoe,  118  ;  Prout's 
hypothesis,  152. 

Patterson,  C.  C,  Walsh,  J.  W.  T..  and 
lliggins.  W.  F.,  radium  luminous 
paint,  54. 

Perrin,  J.,  radiation  theory  of  chem- 
ical action,  145. 

Pinlus,  A.,  ionization  by  gas  reactions, 
129. 

Planck.   M.,  quantum   theory,   132. 

Plotnikow.  .T.,  photochemistry,  7  :  phot- 
oxidation  of  hydriodic  acid,  137  ;  of 
io<Joform,  137, 


INDEX  OF  AUTHORS 


181 


Pohl,  R.,  decomposition  of  ammonia  by 
electrical  discharge,  126. 

Prout,  W.,  atomic  hypothesis,  152. 

Przibram,  K.     See  Meyer,  S.,  50,  51. 

Pusch,  Frl.  L.,  test  of  Einstein  photo- 
chemical law,  136,  138. 

Ramsay,  W.,  excess  of  hydrogen  in 
water  decomposition  by  radium,  48, 
60  :  gas  pipette,  66. 

Ramsay,  W.  See  Cameron,  A.  T., 
66-9,  85,  97,  98. 

Ramsay,  W.,  and  Soddy,  F.,  decom- 
position of  radium  solution,  75. 

Reboul,  G.,  ionization  by  chemical  ac- 
tion, 129. 

Regener,  E.,  photochemical  ozonization, 
134  ;  photolysis  of  ammonia,  134  ;  of 
ozone,  137. 

Reynolds,  E.,  triad  of  neon,  151. 

Rice.  J.,  equation  of  energy  increment, 
143. 

Richards,  T.  W.,  and  Hall,  N.  F.,  in- 
separability of  isotopes,  154. 

Rideal,  E.  K.,  radiation  in  chemical 
kinetics,  146. 

Rideal,  E.  K.,  and  Kunz,  J.,  ozoniza- 
tion in  the  corona,  81,  125. 

Rideal,  E.  K.,  and  Taylor,  tl.  S.,  ca- 
talysis, 144. 

Ringer,  W.  E.  See  Jorissen,  W.  P.,  47, 
85,  119. 

Roberts,  L.  D.,  average  path  of  a  par- 
ticles in  cylinders,  83. 

Robinson,  H.  See  H.  G.  J.  Moseley, 
42. 

Roentgen,  W.  C,  discovery  of  X  rays, 
20,  44. 

Roscoe,  H.  E.     See  Bunsen,  R.,  118. 

Ross,  W.  H.,  photochemical  reduction 
of  ferrous  sulfate.  63. 

Royds,  T.  See  Rutherford,  E.  E.,  22, 
76. 

Runge,  G..  and  BodlSnder,  G..  excess 
hydrogen  in  water  decomposition  by 
radium,  60. 

Russ,  S.,  and  Makower,  W.,  recoil 
atoms  from  a  particles,  154. 

Russell,  A.  S..  change  of  valence  by  a 
or  )3  radiation,  42. 

Rutherford,  E.  E.,  radioactivity,  8,  24  : 
magnetic  and  electrical  deflection  of 
a  parficles.  22  ;  atomic  disruption, 
22  ;  radioactive  equilibrium.  25  ; 
atomic  model.  27  ;  energy  of  ioniza- 
tion, 29  ;  enumeration  of  a  particles, 
31  ;  energy  radiated  by  a,  ^.  and  7 
rays.  42  ;  disintegration  of  quartz  by 
radium  rays.  49  ;  pleochroic  rings  in 
mica,  52  ;  active  centers  of  lumines- 
cence. 54.  57  ;  heat  of  absorption  of 
a,  j8.  and  y  rays,  65  ;  7  ray  deter- 
mination of  emanation,  77 ;  dis- 
appearance of  emanation  in  spec- 
trum tubes,  127  ;  momentum  of  a 
recoil,  155  ;  scattering  of  a  particles, 
162 ;  swift  hydrogen  atoms.  164  ; 
from  nitrogen,  167  ;  swift  helium 
atoms  from  oxygen  and  nitrogen, 
167  ;  helium  atoms  of  mass,  3,  167  ; 
gain  in  energy  by  atomic  disruption, 
166  ;  quantity  of.  168  ;  unclear  struc- 
ture of  nitrogen,  oxygen,  and  car- 
bon atoms,  167. 

Rutherford.  E.  E..  and  Goigor,  IT., 
charge  of  a  particle.  22;  distribution 
of  a  radiation  in  time  and  space,  36. 

Rutherford,  E.  E.,  and  Royds,  T.,  na- 
ture of  a  particles,  22  ;  thin  a  ray 
papjllarjr,  76, 


Rutherford,  E.  E.,  and  Soddy,  F.,  hy- 
pothesis of  atomic  disintegration,  21, 
24. 

Ryde.  J.  W.  H.  See  Campbell,  N.  R„ 
127, 

Sadler,  C.  A.,  characteristic  X  rays,  45. 

Scheuer,  O.,  calculation  of  ionization, 
84 ;  synthesis  of  water  by  emana- 
tion, 85,  89 ;  reduction  of  carbon 
monoxide   (emanation),  90, 

Scheuer,  O.  See  Duane,  W.,  60,  85,  86, 
85-9,   120. 

Schlundt,  H.     See  Leaming,  T.  H.,  66. 

Schmidt,  G.  C.  See  Wiedemann,  E., 
57. 

V.  Schweidler,  E.  See  Meyer,  S.,  8,  24, 
26    155 

Seboi*,  J.  '  See  Stoklasa,  J.,  90. 

Sheppard,  S.  E.,  photochemistry,  7. 

Shimizu,  T.     See  Duane,  W.,  45. 

Siegbahn,  M.,  X  radiation,  45. 

Soddy,  F.,  change  of  valence  by  a  or 
P  radiation,  42  ;  theory  of  isotopic 
separation.  154. 

Soddy,  F.     See  Ramsay.  W.,  75. 

Soddy,  F.  See  Rutherford,  E.  E.,  21, 
24. 

Stark,  J.,  loosening  of  valence  elec- 
trons, 134,  140. 

Stoklasa,  J.,  Sebor,  J.,  and  Zdobnicky, 
v.,  reduction  of  carbon  monoxide  by 
hydrogen    (radium),  90. 

Strong,  W.  W..  theory  of  ozone  forma- 
tion, 81,  123. 

Strutt,  R.  J.,  positive  charge  of  a  par- 
ticle, 22. 

Taylor,  IT.  S.,  regulator  for  thin  o  ray 
bulb,  79  ;  synthesis  of  hydrogen  chlo- 
ride by  a  rays.  85,  119  ;  non-exist- 
ence of»active  molecules.  143. 

Taylor,  H.  S.  See  Rideal,  E.  K., 
144. 

Taylor,  T,  S.,  specific  ionization  of 
gases  by  a  rays,  92. 

Thomson.  J.  J.,  positive  rays,  148  ;  va- 
riety of  gaseous  ions,  81  ;  absence  of 
ions  in  photo-synthesis  of  hydrogen 
chloride.  128 ;  analysis  by  positive 
rays,  149. 

Tian.  A.,  nhotolysis  of  hydrogen  perox- 
ide. 137. 

Tolman.  R.  C,  radiation  and  chemical 
kinetics,  146. 

Townscnd.  J.  S.,  ionization  by  collision, 
43.  124 ;  rate  of  recombination  of 
gas  ions.  117. 

Trautz.  M..  radiation  theory  of  ca- 
talysis.  144. 

Trnutz,  M..  and  Bhandarkar,  D.  S., 
decomposition  of  phosphine,  145. 

Underwood,  J.  E.  See  Leaming,  T.  H., 
66. 

Usher,  F.  L.,  non-catalytic  action  of  a 
rays.  59  ;  ammonia  equilibrium  (em- 
anation), 72;  decomposition  of  am- 
monia and  water  by  emanation,  85, 
98  :  absorption  of  hydrogen  by  glass 
under  a  radiation,  112  ;  decomposi- 
tion of  water  by  a  and  by  P  rays, 
113. 


Vollmer,  M.     See  Le  Blanc,  M.,  128. 

Waentig,    P..    phosphorescent    alkaligp 
parth  s\ilfldps,  57, 


1S2 


INDEX  OF  AUTHORS 


Walsh,  J.  W.  T.,  recovery  of  luminos- 
ity of  radium  paint,  54 ;  meso- 
thorium  luminous  paint,  55. 

Walsh,  J.  W.  T.  See  Patterson,  C.  C, 
54. 

Walter,  B„  life  of  radiothorium,  55. 

Warburg,  E.,  low  energy  utilization  in 
photochemical  action,  123  ;  inapplica- 
bility of  Faraday's  law  to  ozoniza- 
tion  by  electrical  discharge,  124 
test  of  Einstein's  law,  132,  139; 
photochemical  ozonization,  134  ;  pho 
tolysis   of  ammonia,    134. 

Weigert,  P.,  photochemistry,  7 ;  pho- 
tolysis or  ozone  by  chlorine,  134 ; 
without  chlorine,  137. 

Weigert,  F.,  and  Kummerer,  L.,  photo- 
chemical conversion,  134. 

Weigert,  F.     See  Luther,  R.,  134. 

Wellisch,  E.  M.,  cluster  ions,  81. 

Wendt,  G.  L.,  and  Landauer,  R.  S., 
cluster  ions,  81 ;  tri-atomic  hydro- 
gen,  112. 

Wendt,  G.  L.    See  Duane,  W.,  112. 

Wertenstein,  L.,  a  recoil  atoms,  155, 
159. 


Wiedemann,  E.,  and  Schmidt,  G.  C, 
phosphorescent  alkaline  earth  sul- 
fides, 57. 

Wien,  W.,  magnetic  deflection  of  canal 
rays,  148. 

Wigand,  A.,  photochemical  transforma- 
tion of  sulfur,  134. 

Wildermann,  M.,  photo-synthesis  of 
phosgene,  138. 

Winther,  C,  bleaching  of  dyes,  137. 

Wood,  A.     See  Campbell,   N.   R.,  24. 

W^oudstra,  H.  W.  See  Jorissen,  W.  P., 
47. 

Wourtzel,  E.  E.,  ammonia  decomposi- 
tion by  one  a  particle,  73  ;  extrapola- 
tion of  ionization,  84  ;  decomposition 
of  hydrogen  sulfide,  ammonia,  nitrous 
oxide,  and  carbon  dioxide  by  emana- 
tion, 85,  93,  121 ;  inapplicability  of 
thermal  theory  of  a  ray  chemical 
effect,  116  ;  no  synthesis  of  ammonia 
by  emanation,  85,  120  ;  collision  the- 
ory or  radiochemical  action,  93. 

Wurmser,  R.     See  Henri,  V.,  137,  145. 

Zdobnicliy,  V.     See  Stoklasa,  J.,  90. 


I 


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The  chemical  effects 
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^Ve  chmical  effects 
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